Filesize is on original jpg small enough – so you can insert the full image. Maybe that is a bit sharper then.

And maybe you switch earlier to hamburger menu :

@media only screen and (max-width: 1200px) {
    #top #header .av-main-nav > li.menu-item  {
        display: none!important;
    }
    #top #header .av-burger-menu-main {
        cursor: pointer;
        display: block!important;
    }
}

if your graphic designer got a vectorgraphic of it this will be sharper than a png file. He should offer it as svg graphic.
btw. a png file is usefull if there are transparencies (f.e. the pure green logo without background) so here is a cropped logo as jpg – you can use it for now.

download it here as zip file: https://webers-testseite.de/First_business_card_5.jpg.zip

on your landing page (no enfold page ) or on the other pages?
(ok www leads to a different landing page )

First hint – your logo got quite a lot of white space around the green logo inside.
So unless the corporate design specifies that there should be so much white space around the actual logo, I would change that first.

Would you like to hide only the logo image or both the logo image and navigation?
Would you like to hide it on small screen sizes or exclusively on mobile devices?

you can use even colorized svgs if you just upload them to media-library.
On media-library list view – you see the ID of that svg file – note it for the code snippet:

add this to your child-theme functions.php:
(change the 49551 to your ID)

function avia_add_custom_icons($icons){
  $icons['bluesky'] =  array( 'font' =>'svg_wp-media-library', 'icon' => '49551', 'display_name' => 'Bluesky');
    return $icons;
  }
add_filter('avf_default_icons','avia_add_custom_icons', 10, 1);

function avia_add_custom_social_icon($icons){
    $icons['bluesky'] = 'bluesky';
    return $icons;
}
add_filter('avf_social_icons_options', 'avia_add_custom_social_icon', 10, 1);

you will find then the bluesky at the end of the drop-down list where all the others are.
Important: pay attention that your uploaded svg file is not a svg with height/width settings but with viewport.

bluesky svg link

or you can transform your svg on svgomg

ok – this seems to be enough inside child-theme functions.php:

add_filter("avf_ajax_preview_image_size", function($size) {
   $size = "full";
   return $size;
}, 10, 1);

Are these self-hosted videos? How large are the files?

PS : you should use for the thumbnails in the grid recalculated smaller images e.g.

you are now using the full image (no-scaling).

can we influence the image shown in the ajax preview ( that img insided avia-gallery-big ) – it seems to use the recalculated “large” image.
But as you know this might be bigger in file size than the original uploaded image!
I can not find a filter to adjust it.

or could we influence it by
$params['preview_size'] = apply_filters( 'avf_ajax_preview_image_size', 'gallery' );

i can find this in portfolio.php

//	create array with responsive info for lightbox
	$img = Av_Responsive_Images()->responsive_image_src( $attachment->ID, 'large' );

bring it to full will often reduce file-size – as you know that Enfold standard compression leads to bigger file-sizes on large image.

ok – i found the place to change in gallery.php (line 757)
$prev = wp_get_attachment_image_src( $attachment->ID, $preview_size );

if we would use :
$prev = wp_get_attachment_image_src( $attachment->ID, 'full' );

looking to his page f.e.:
the krebs-treppen-systeme-gelaender-system30-3.jpg is 121kb
but krebs-treppen-systeme-gelaender-system30-3-1030×839.jpg is 268kb

the whole page got over 112MB images – and could be reduced to a half size.

maybe this gives you some hints how it could be obtained: https://kriesi.at/support/topic/the-website-loads-invisible-elements/#post-1490800

This is an Enfold CSS that controls the respective element.
In this case it can be found here: /enfold/config-templatebuilder/avia-shortcodes/testimonials
But at least the Quick CSS variant will remain intact when you update Enfold.

have you followed my link to the testpage? There is the video in the “background!” you can see the layout of that in the placed image below.
The rest is the css you need.
PS: Hope Mike could help you – because as a participant i can not see private content area.

see my edit above – posting the same time

try:

#top picture.avia_image {
  display: flex !important;
}

and maybe you like to have more contrast on hovering the images:

#top a.avia_image .av-image-caption-overlay-center {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  display:  grid;
  margin: 5px 25px;
  font-size: 1.2em
}

#top a.avia_image:hover .av-image-caption-overlay-center {
  color: #940000;
  background-color: rgba(255,255,255,0.6);
  backdrop-filter: blur(4px);
}

#top .av-image-caption-overlay-center p {
  margin: 10px 0 !important;
}

Yes – as mentioned above : If the video file-size is not big – the best performance will be to self-host the video.

the filter avf_logo_subtext is nice to have both Logo Image and Text

try instead:

function use_text_logo_only($logo){
  $link = apply_filters( 'avf_logo_link', home_url( '/' ) );
  $logo_tag = "h1";
  $logo_heading = "Wayne Anderson";
  $alt = get_bloginfo( 'name' );    
  $title = get_bloginfo( 'name' );

  $logo = '<a class="logo text-logo" href="'.$link.'" alt="'.$alt.'" title="'.$title.'"><'.$logo_tag.'>'  .$logo_heading.'</'.$logo_tag.'></a>';
  return $logo;
}
add_filter('avf_logo_final_output','use_text_logo_only');

and on quick css:
(maybe with your header setting – you had to adjust the css a little bit )

#top .logo.text-logo  {
  display: flex;
  justify-content: left;
  align-items: center;
  width: auto;
}
#top .logo.text-logo h1  {
  margin: 0 !important;
  font-size: 30px;  /* adjust to your needs */
  text-transform: uppercase !important;
}

PS: if you like to have different alt and title tags replace in the snippet above with hardcoded strings

$alt = "your alt attribute";    
$title = "your title attribute";

and if you do not like to have a h1 – just replace to a different tag ( h2, div, span etc. ) but then you had to adjust the css to that tag

see example page: https://webers-testseite.de/background-video/