yes: this is not a warning that you have activated the self-destruction button : it might break !

Warning: Characters <,>,[,] might break ALB backend or frontend. Read more if you want to use them. You can use valid HTML markup.

And you see in detail what characters could indicate that. – those which are correlated with code ( tags etc. )

There must be a conflict that may have nothing to do with Enfold. Forcing a jpg or a pdf download is more complex, but a zip is actually always made available for download automatically.
Your page above is inaccessible.

when you are in editor mode and have your Advanced Layout Builder open – click that sign besides templates:

here you are. After editing you have on top right these three buttons Preview, Update and Close.

yes – but this additional information would not have been bad to know at the beginning.

So best would be to use the normal Enfold Background-Image Insertion by the ALB Element itself – and then bring some dividers on top f.e. by custom class.

This will be best – by handling svgs inserted by a custom class of the color-section to the right place in the dom
This might be the best place for it: https://kriesi.at/support/topic/curved-section-dividers/#post-1212353
If you do it the right way – even animated svgs could be inserted: see the bottom of that page: https://webers-testseite.de/pureinstall/fullwidth-slider/

A littel help is here: https://kriesi.at/support/topic/diagonal-border-angle/#post-1138048

but this will be more a tutorial here then a little help.
Get familiar with svg and and … sorry to much to say here .

As you can see on my test page and in the instructions if you got 2 images in one container as background – you can have 2 instructions each for:
background-position, background-size, background-repeat etc. pp. every background value can be twice same separated by commata.

i do not see on your page that custom class: blog-divider – so it is hard to give advice.

on my test-page from above i put in my page your images – and here is the code for that page:
https://webers-testseite.de/multiple-background-images/#av_section_4

.page-id-30559 .three-bg-images {
    background-image: 
     url("/wp-content/uploads/double-wabe-bot.png" ), 
     url("/wp-content/uploads/bandeau_1920.jpg" ) , 
     url("/wp-content/uploads/clinique-synapse-comprendre-la-douleur-chronique.jpg"  ) ;
    background-repeat: no-repeat;
    background-position: left bottom, left top, center center;
    background-size: contain , 100% 20px ,  cover;
}

These are layered atop one another with the first background you provide on top and the last background listed in the back. Only the last background can include a background color.

if you got for all the same value ( like above – background-repeat – you can write down shorten : background-repeat: no-repeat)

by the way – more complex – something for techies ;)
a second footer row – with admin options to style – either in the footer a second footer row – or in the socket one! ;)

https://kriesi.at/support/topic/second-widget-line-in-footer/

for text you can use a min max combination for font-size :

f.e.:
font-size: min(max(28px,2.4vw),42px) !important;

see here: https://css-tricks.com/how-do-you-do-max-font-size-in-css/
and
https://css-tricks.com/snippets/css/fluid-typography/

you can add a lot of additional settings above

$header['header_shrinking']   =  'header_shrinking';
$header['header_class'] .= " av_header_shrinking";

or

$header['header_transparency'] = 'header_transparency';
$header['header_class'] .= " av_header_transparency";

but some of the settings are mutually exclusive. So I don’t know if a header on the left with a transparent header makes sense.

A custom color scheme you can have by this in your child-theme functions.php and the filter: avf_skin_options
( you find the existing color-schemes in folder: enfold – includes – admin : register-backend-styles.php
but that would not help you to have on page1 that color-scheme and on a different page the other.

function my_custom_added_style_function($styles = "") {

  $default_primary  = "#2d5c88";
  $default_highlight  = "#3d71a1";
  $default_background = "#041424";
  $special_border   = "#0A2138";

//put your own Name for the style
  $styles["Guennis Style"] = array(    
              "style"=>"background-color:$default_primary;",
              "default_font" => "Open Sans:400,600",
              "google_webfont" => "Open Sans:400,600",
              "color_scheme"  =>"Guennis Style",
              
              // header
              "colorset-header_color-bg"        =>"#ffffff",
              "colorset-header_color-bg2"       =>"#f8f8f8",
              "colorset-header_color-primary"     =>"$default_primary",
              "colorset-header_color-secondary"   =>"#444444",
              "colorset-header_color-color"     =>"#333333",
              "colorset-header_color-border"      =>"#e1e1e1",
              "colorset-header_color-img"       =>"",
              "colorset-header_color-customimage"   =>"",
              "colorset-header_color-pos"       => "top center",
              "colorset-header_color-repeat"      => "repeat",
              "colorset-header_color-attach"      => "scroll",
              'colorset-header_color-heading'     => '#000000',
              'colorset-header_color-meta'      => '#808080',
              
              // main
              "colorset-main_color-bg"        =>"#ffffff",
              "colorset-main_color-bg2"       =>"#fcfcfc",
              "colorset-main_color-primary"     =>"$default_primary",
              "colorset-main_color-secondary"     =>"$default_highlight",
              "colorset-main_color-color"       =>"#666666",
              "colorset-main_color-border"      =>"#e1e1e1",
              "colorset-main_color-img"       =>"",
              "colorset-main_color-customimage"   =>"",
              "colorset-main_color-pos"         => "top center",
              "colorset-main_color-repeat"      => "repeat",
              "colorset-main_color-attach"      => "scroll",
              'colorset-main_color-heading'       => '#222222',
              'colorset-main_color-meta'        => '#919191',
              
              // alternate
              "colorset-alternate_color-bg"     =>"#fcfcfc",
              "colorset-alternate_color-bg2"      =>"#ffffff",
              "colorset-alternate_color-primary"    =>"$default_primary",
              "colorset-alternate_color-secondary"  =>"$default_highlight",
              "colorset-alternate_color-color"    =>"#666666",
              "colorset-alternate_color-border"   =>"#e1e1e1",
              "colorset-alternate_color-img"      => "",
              "colorset-alternate_color-customimage"  =>"",
              "colorset-alternate_color-pos"      => "top center",
              "colorset-alternate_color-repeat"     => "repeat",
              "colorset-alternate_color-attach"     => "scroll",
              'colorset-alternate_color-heading'    => '#222222',
              'colorset-alternate_color-meta'     => '#8f8f8f',
                          
              // Footer
              "colorset-footer_color-bg"        =>"#222222",
              "colorset-footer_color-bg2"       =>"#333333",
              "colorset-footer_color-primary"     =>"#ffffff",
              "colorset-footer_color-secondary"   =>"#aaaaaa",
              "colorset-footer_color-color"     =>"#dddddd",
              "colorset-footer_color-border"      =>"#444444",
              "colorset-footer_color-img"       => "",
              "colorset-footer_color-customimage"   =>"",
              "colorset-footer_color-pos"       => "top center",
              "colorset-footer_color-repeat"      => "repeat",
              "colorset-footer_color-attach"      => "scroll",
              'colorset-footer_color-heading'     => '#919191',
              'colorset-footer_color-meta'      => '#919191',
              
              // Socket
              "colorset-socket_color-bg"        =>"#333333",
              "colorset-socket_color-bg2"       =>"#555555",
              "colorset-socket_color-primary"     =>"#ffffff",
              "colorset-socket_color-secondary"   =>"#aaaaaa",
              "colorset-socket_color-color"     =>"#eeeeee",
              "colorset-socket_color-border"      =>"#444444",
              "colorset-socket_color-img"       =>"",
              "colorset-socket_color-customimage"   =>"",
              "colorset-socket_color-pos"       => "top center",
              "colorset-socket_color-repeat"      => "repeat",
              "colorset-socket_color-attach"      => "scroll",
              'colorset-socket_color-heading'     => '#ffffff',
              'colorset-socket_color-meta'      => '#999999',
              
              //body bg
              "color-body_style"            =>"stretched",
              "color-body_color"            =>"#333333", //bg
              "color-body_fontcolor"          =>"#ffffff", //font
              "color-body_attach"           =>"scroll",
              "color-body_repeat"           =>"repeat",
              "color-body_pos"            =>"top center",
              "color-body_img"            => "",
              "color-body_customimage"        =>"",
              
  );
  
  return $styles;
}
add_filter('avf_skin_options', 'my_custom_added_style_function');

what – if you do not use the sidebar on that page – and style it this way:

This will look like a sidebar – but is part of the color-section
So another color-section under it will not influence the behavior above

see here a fullwidth element under the color-section: https://webers-testseite.de/mimic/

Why is it fixed on safari and on other browsers not – there it scrolls.
Safari is one browser that can not handle good the css with background-attachment : fixed.
there are workarounds here on board – to set the background-attachment : scroll and place a pseudo-container with the inherited image as background and place the pseudo-container on position : fixed

Edit – may i ask you why you had to work with the slider? and not with a 100% color-section. this Element is not so performance intensive.
have a look at: https://webers-testseite.de/jaime/ – with safari

/*********** Safari Fix for background-attachment: fixed  **************/
/********* give a custom-class to the color-section:   bg-fixed  ***********/
/***** Set the image to background-attachment : scroll and :  **********/

.avia-section.bg-fixed  {
	-webkit-clip-path: inset(0 0 0 0);
	clip-path: inset(0 0 0 0);
	background-size: 0 !important;
	overflow: hidden;
	position: relative;
}

.avia-section.bg-fixed:before {
  background-image: inherit !important;
  background-repeat: inherit !important;
  background-size: cover;
  background-position: inherit;
  content: "";
  position: fixed;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  z-index: -1 !important;
  pointer-events: none;
  will-change: transform;  /*** if you got more than 3 images like this - comment this out ***/
}

maybe 6 columns break to one column is a bad responsive behavior – so go and flex the layout for it f.e.:
in quick css:

#footer .container {
  display: flex;
  flex-flow: row wrap;
  justify-content: space-between;
}

#footer .flex_column {
  width: unset !important;
  flex: 0 1 14%;
  margin-left: 0;
}

@media only screen and (max-width:1249px) {
	#footer .flex_column {
	  width: unset !important;
	  flex: 0 1 30%;
	}
}

@media only screen and (max-width:989px) {
	#footer .flex_column {
	  width: unset !important;
	  flex: 0 1 50%;
	}
}

@media only screen and (max-width:767px) {
	#footer .flex_column {
	  width: unset !important;
	  flex: 0 1 100%;
	}
}

ok – you mean this enfold feature ( yellow underlined in the image) not the tooltip ( red-underlined)

hey mike you can find here account info: https://kriesi.at/support/topic/customized-lightbox-markup/#post-1286046

I had understood him/her to mean that different ALB elements should form a gallery with images in a common lightbox. Also the images that were inserted in a text box, for example.