Well – if that is what I think you want, then there is no trivial solution.
i did it here for very small screens (mobile device screen width) on : https://guenterweber.com/datenschutz/
because the widget ( second menu) on that page needs more place – that is not there on small screens.

Base of even the Enfold Hamburger (av-hamburger–spin) for main-menu is : https://jonsuh.com/hamburgers/

do not forget that on jQuery 3.x the

jQuery(window).load(function(){

is deprecated – it has to be now:

$(window).on('load', function(){

in addition to that – why do you like to open a different page in the lightbox?
do you have on many pages that button?

big hussle is that it is no button element – it is an input – with button functionality.
if it is a button tag – then styling is much easier.

you can change that by child-theme functions.php snippet:

function change_input_to_button_tag(){
?>
<script>
  (function($) {       
      function replaceElementTag(targetSelector, newTagString) {
        $(targetSelector).each(function(){
          var inputvalue = $(this).attr('value');
          var newElem = $(newTagString, {html: $(this).html()});
          $.each(this.attributes, function() {
            newElem.attr(this.name, this.value);
          });
          $(this).replaceWith(newElem);
          newElem.append('<span class="submit">'+inputvalue+'</span>');
        });
      }
      replaceElementTag('.avia_ajax_form input.button', '<button></button>');
  }(jQuery)); 
</script>
<?php
}
add_action('wp_footer', 'change_input_to_button_tag');

have a look on that page – open editor – on the right side there are layout options – including a part for footer setting and footer behaviour.

Unfortunately, exactly this option is missing – only display the socket and hide the footer page.
There is probably no other option than to set the footer page to display none with the page ID.

f.e.:

#top.page-id-3 #footer-page {
  display: none;
}

a fast way might be to only replace the content:

#scroll-top-link[data-av_icon]::before {
  content: url(/wp-content/uploads/myTest.svg);
}

But I only tested it with an svg file, so I had no problems getting the dimensions to fit.

this is very nice !

on mobile we have this behaviour (close on click outside) already – because of Content Setting : “Mobile Close Behaviour”
does your script interfere with it?
On mobile even a click on a different Flip-Card closes the other ones. ( that is my prefered behavior) and closes all on clicking outside.

maybe it has to do with the default strip_tags option on many excerpts ( post_excerpt )
or that function avia_backend_truncate often used in enfold to filter strings.

PS try <strong> instead of <b>
strong , em and span are excluded tags from strip_tags

i would prefer this solution:

#top.page-id-102 #av_section_1 .flex_column img {
  -webkit-filter: brightness(0.6) blur(3px);
  filter: brightness(0.6) blur(3px);
  transition: filter 1s ease;
}

#top.page-id-102 #av_section_1 .flex_column:hover img {
  -webkit-filter: brightness(0.8) blur(0px);
  filter: brightness(0.8) blur(0px);
  transition: filter 1s ease;
} 

ok – if there is no easy way. Just switch for a short moment to:
General Layout : Top Header
Go to “Header – Extra Elements and choose on Enfold WPML Language Flags (Global Setting) : hide …
Switch back to your “Left Sidebar Header”
Save the settings

Now insert this to your child-theme functions.php:

add_action('ava_main_header_sidebar', function() {
  echo do_shortcode("[wpml_language_selector_widget]");
});

And now style it via WPML – Languages – Custom language switchers

DOM will look like this then:

What font do you like to upload?

long time ago – and with some changes ( for example the possibility to upload variable fonts ) you can read here a more detailed instruction:
https://kriesi.at/support/topic/host-web-font-yourself-some-info/#post-1364066
And: a tip if it is realy neccessary to have a specific italic typeface.

can you please remove the css code from Ismael and insert instead :
( because of .avia-slideshow-carousel must stay overflow: hidden – the left arrow is not visible )

@media only screen and (min-width: 990px) {
  .avia-timeline-container {
    padding: 0 40px;
  }

  .av-timeline-nav {
    padding-top: 0px;
    width: 100%;
    overflow: visible !important;
  }

  #top .avia-timeline-container.av-slideshow-ui .avia-slideshow-arrows.av-visible-next > a.next-slide {
    position: absolute;
    top: 0px;
  }

  #top .avia-timeline-container.av-slideshow-ui .avia-slideshow-arrows.av-visible-prev > a.prev-slide {
    position: absolute;
    top: 0px;
  }
}

maybe you like to include to that media-query a setting to have more space for the :

.avia-timeline-horizontal.av-milestone-placement-top .av-milestone-content-wrap {
  padding: 30px 15px 10px 80px;
}

after that we can see if we need to fix some other settings.

I don’t believe that only Google Fonts can be uploaded.
I have successfully uploaded several premium fonts from Adobe, Bitstream, Elsner & Flake etc. pp. after converting them to web font formats. In the meantime I only prefer woff2 (for older browsers I usually add the ttf files)

try to upload otf files to tranfonter page: Link

Big Advantage on Transfonter Page is the family support.

if there are troubles in rendering the font – ( what OS X do you use on your device) you can include the other font formats too
but with ttf you got a good old browser support.
Browser Support

#top #avia-menu .avia-menu-fx {
  background-color: #8c084c
}

if the html lang attribute changes to the new language – the labels are not translated?
does your lang plugin set a html lang attribute?

_________
anyway:
give a unique ID to your countdown element f.e.: spanish

then follow the exemple here: https://enfold.webers-webdesign.de/3-columns/

for child-theme functions.php:

function set_spanish_translations(){
?>
<script>
window.addEventListener("DOMContentLoaded", function () { 
	(function($) {       
		$('#spanish').attr('lang', 'es-ES');
		$('#spanish .av-countdown-years .av-countdown-time-label').attr({'data-label': 'Año', 'data-label-multi': 'Años'});
		$('#spanish .av-countdown-months .av-countdown-time-label').attr({'data-label': 'Mes','data-label-multi': 'Meses'});
		$('#spanish .av-countdown-weeks .av-countdown-time-label').attr({'data-label': 'Semana','data-label-multi': 'Semanas'});
		$('#spanish .av-countdown-days .av-countdown-time-label').attr({'data-label': 'Día','data-label-multi': 'Días'});
		$('#spanish .av-countdown-hours .av-countdown-time-label').attr({'data-label': 'Hora','data-label-multi': 'Horas'});
		$('#spanish .av-countdown-minutes .av-countdown-time-label').attr({'data-label': 'Minuto','data-label-multi': 'Minutos'});
		$('#spanish .av-countdown-seconds .av-countdown-time-label').attr({'data-label': 'Segundo','data-label-multi': 'Segundos'});
	}(jQuery)); 
});
</script>
<?php
}
add_action('wp_footer', 'set_spanish_translations');

it differs between data-label and data-label-multi – for singular and plural form of the Units