iFrames and lightbox for various views

the easiest way would be: if devs could create a conditional input field as soon as you have selected lightbox as the destination, in which you can enter the mfp type as a link class – because:
By default, Magnific Popup has four types of content: image, iframe, inline, and ajax ( classes: mfp-image, mfp-iframe, mfp-inline, mfp-ajas) . There is no any “auto-detection” of type based on URL, so you should define it manually.
But that had to be tested if that will be enough to rule the grouping between mixed content.

ok – if i place those images with different links inside a text-block – i can force that behaviour by adding the link class: mfp-iframe and as rel: lightbox.
see the script – avia-snippet-lightbox.js – a[rel^="lightbox"] – is an autolink element (autolinkElements)

Edit: a solution for masonry is shown on that test-page : https://webers-testseite.de/mixed-lightbox-content/

yes but i suppose that then the av-masonry-entry is not the right selector too.
What kind of element do you use?
Inspect your page with developer tools and have a look what class the link itself has – on masonry it is av-masonry-entry.

On Portfolio Grid – you had choosen the Option : !Open a preview of the entry (known as AJAX Portfolio)” these are totaly different settings. Choose “Open in lightbox” then we can talk about mixed content.
The custom link could be done on the portfolio page itself – via “Additional Portfolio Settings” !

etc. Each of those elements need an own solution. – sometimes there had to be a preventDefault or a stopPropagation of the existing event.

Dear luleloki – i’m Participant as you are – so i do not see private content area.

this is based on the snippet above. – but you had to be aware that portfolio links are all url links – so the link goes then to the lightbox – and not to the portfolio page.
You could possibly check whether it is an internal link or not.

the snippet looks to the anchor – and to its href – if href is an image link – then all stayes as it is – if not …

function lightbox_with_mixed_content_type() { 
?>
<script type="text/javascript">
window.addEventListener("DOMContentLoaded", function () { 
	(function($){
		$('.mixed-contenttype a').each(function(){
			var anchorLink = $(this).attr('href');
			if (/\.(jpg|png|gif|webp|jpeg)$/.test(anchorLink)) {
				//console.log(anchorLink + " is an image link");
			} else {
				$(this).attr('rel', 'lightbox').addClass('mfp-iframe');
			}
		});	
	})(jQuery);
});
</script>
<?php 
}
add_action('wp_footer', 'lightbox_with_mixed_content_type', 999);

but as mentioned above – the ajax portfolio grid will not do that .