i try to edit the xml file but all but one is good working.
I could not find the settings for the blog page to edit in the right manner.
so dear mods it is time to prepare the old xml files to the new https sources.

just wait

to have the kriesi links in your installation ( but you have to replace it later to your own copies or new images) you can do this:

what you can do now:
install this nice plugin: https://wordpress.org/plugins/search-and-replace/

The thing is that on the old demo the links are on http places. But it seems that the base url is always the same
So after installing that plugin.

• Open it via dashboard – tools – search and replace
• save your Database first – create sql file
• then go to tab: search & replace
• put in the field search for: http://test.kriesi.at/new-spa/wp-content/uploads/sites/11/2015
• put in the field replace with: https://kriesi.at/themes/enfold-spa/wp-content/uploads/sites/56/2015
• mark all tables and “do search and replace” by writing to database

looks this way:
(click to enlarge)

After that you can deactivate the plugin and deinstall it.

Concerning to your heading on the topic:
If he has no proof of purchase – you can delete the calculated Envato Personal Token Key ( from Enfold Options ) and better : on Envato create a new token

Kardinal Frage: meinst du auch wirklich Mobile Endgeräte ? oder ist viel eher für kleine Screenbreiten gedacht?
Wenn es für Mobile Endgeräte sein soll, dann solltest du auch da prüfen, und nicht nur das Browserfenster schmal ziehen.

(Cardinal question: do you really mean mobile devices? or is it much more intended for small screen widths?
If it should be for mobile devices, then you should also check there, and not just narrow the browser window.)

Der Code von Ismael ist für das child-theme functions.php gedacht. ( und für Mobile Endgeräte gedacht)
wobei ich mir mal einen etwas kürzeren Code notiert hatte:

Es hängt jetzt aber auch viel von deiner Seite ab. Daher wäre ein livelink sehr gut.
Denn wenn du zB die transparent header Variante wählst, dann ist das Logo ein anderes.

function avia_custom_mobile_logo(){
if(wp_is_mobile()){
?>
<script>
(function($){
	$(".logo img").attr("src", "http://kriesi.at/wp-content/themes/kriesi/images/logo.png");
})(jQuery);
</script>
<?php
}
}
add_action('wp_footer', 'avia_custom_mobile_logo');

Wenn du es nur für schmale Screenbreiten brauchst ( ist dann ja auch bei Mobilen Endgeräten aktiv) wäre das hier ein Code:
( die 480px sind hier mal als Grenze gesetzt – kannst Du aber anpassen)

function custom_logo_for_small_screens(){
?>
<script>
(function($){
	$(window).load(function(){
	if ($(window).width() < 480) {
		$(".logo img").attr("src", "http://kriesi.at/wp-content/themes/kriesi/images/logo.png");}
	});
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'custom_logo_for_small_screens');

PS @ismael : there is this navigator.userAgent query in avia.js directly at the beginning. Yours looks very extensive; could we replace it with your detailed one in the combination with && 'ontouchstart' in document.documentElement ?

But please read carefully.

Recommendations

Add rel=”noopener” or rel=”noreferrer” to each of the links that Lighthouse has identified in your report. In general, when you use target=”_blank”, always add rel=”noopener” or rel=”noreferrer”.

Or : means – nofollow will be enough to add.

btw: you can reach this via child-theme functions.php
adjust the webers-testseite.de through your home domain url:

add_action('wp_footer', 'open_external_links_in_newtab');
function open_external_links_in_newtab(){
?>
<script type="text/javascript">
(function($) {
	$('a').not('a[href*="webers-testseite.de"]').attr({
		'target':'_blank',
		'rel': 'nofollow',
	})
})(jQuery);
</script>
<?php
}

means that any link that does not match your domain url will be considered external and will be opened in a new tab with the attribute nofollow.

it is allways better to have the livelink to say something
but isn’t it the normal behavior to have the image title under the lightbox image?

may i ask before some questions: Did the child-theme has a different – more personalised name?
Where did the infogov_theme come from?

Did you rename your dynamic stylesheet via that known snippet?

add_filter('avia_dyn_stylesheet_file_path', 'avia_change_filename');
function avia_change_filename($stylesheet){
return 'myfilename.css';
}

Wobei da im Regelfall keine Einträge sein sollten/müssen.

you can try this in your child-theme functions.php to place for logo and alternate logo title and alt attributes:

function custom_logo_attriubtes(){
?>
<script>
(function($){
	$('.logo img').attr({ title:"Tobias Glawe Fotografie", alt:"Fotograf Hannover - Tobias Glawe Fotografie" });
	$('.logo img.alternate').attr({ title:"Tobias Glawe Fotografie", alt:"Fotograf Hannover - Tobias Glawe Fotografie" });
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'custom_logo_attriubtes');

First time i recognized this.
But this must be done : i have in my quick css a background set to f.e.:
url(/wp-content/uploads/Seal.png ) and it will end up in: url(/wp-content/uploads/dynamic_avia/Seal.png )
that the merged css is in that folder is ok – but the links to the images are still not in that folder !!!
That is a bug.
I noticed it here first time : https://webers-testseite.de/multiple-background-images/ where there are multiple background-image definitions. When i turn on the merging – the images are not found.
Do i have to address now with absolute path?

Wie hast du das gemacht. Nur die Einträge in den Einstellungen – Allgemein geändert, oder wirklich in der Datenbank.
Weshalb ich frage: Das mit der Datenbank wäre der richtige Weg. Wenn man das machen möchte ohne große mysql Kenntnisse zu haben geht es mit einem kleinen Plugin : Search und Replace
Da kann man die Datenbank zunächst sichern und dann umstellen. Da du aber schon die Url umgestellt hast, ist ein suchen und ersetzen wohl besser dann.
man kann alle Tabellen markieren und dann zB.
http://www.xmpublishing suchen und ersetzen durch:
https://www.xmpublishing

man kann auch erstmal einen Testlauf machen und dann in die Datenbank schreiben.
bei der kompletten Url wird er meckern, da dies für den “Replace Domain Url” vorgesehen ist.
nur https gegen http ersetzen wäre fatal.

F.e. if you like to replace all h2 headings in the slider with h1 – put this into your child-theme functions.php

function replace_tags_with_tags(){
?>
<script>
  (function($) {       
      function replaceElementTag(targetSelector, newTagString) {
        $(targetSelector).each(function(){
          var newElem = $(newTagString, {html: $(this).html()});
          $.each(this.attributes, function() {
            newElem.attr(this.name, this.value);
          });
          $(this).replaceWith(newElem);
        });
      }
      replaceElementTag('.avia-slideshow h2', '<h1></h1>'); 
  }(jQuery)); 
</script>
<?php
}
add_action('wp_footer', 'replace_tags_with_tags');

if you just want this only on that page set an if-clause:

function replace_tags_with_tags(){
if(is_page(504)){
?>
<script>
  (function($) {       
      function replaceElementTag(targetSelector, newTagString) {
        $(targetSelector).each(function(){
          var newElem = $(newTagString, {html: $(this).html()});
          $.each(this.attributes, function() {
            newElem.attr(this.name, this.value);
          });
          $(this).replaceWith(newElem);
        });
      }
      replaceElementTag('.avia-slideshow h2', '<h1></h1>');
  }(jQuery)); 
</script>
<?php
}
}
add_action('wp_footer', 'replace_tags_with_tags');

To explain the behaviour more precisely. If you have only selected Title Display in the settings of the Masonry, this should also apply to the elements that appear after pressing the “Load More” button. However, this is not the case; the title and description are then displayed for those elements.

Enfold in the newer versions ( definitly on 4.5.4 ) got on Theme Options at the bottom: “Select Your Editor” There you have the choice.
By the way: My Recomendation is for the devolopers to set the standard not to ‘ ‘ but to : enable_wp_classic_editor