Youtube video not blocked properly

First, have you checked the box to load thumbnails locally?
under Content Blocker – Youtube – this is besides your question a thing to mention.

_______
what kind of link is it – does it lead to a lightbox with the video? can you show me the site it concerns?

well – borlabs offers an iframe option.

• something like this placed on that page in a codeblock element:
  <div id="youtube-film" class="mfp-hide">[borlabs-cookie id="youtube" type="content-blocker"]<iframe width="100%" height="800" src="https://www.youtube-nocookie.com/embed/Uzjt3fvIlnY" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>[/borlabs-cookie]</div>
  The mfp-hide class will ensure that the div in the codeblock isn’t visible.
• your button is linking to that ID: #youtube-film ( if you got more than one film – each got his own id ) for each a unique div with that id (could be in the same codeblock)
• Give a custom-class to your button!
• Then you had to make your own magnificPopup script to open that class in an inline popup ;)
  the custom-class as trigger with midclick=true, type= 'inline', delegate: 'a', as option

Link
maybe you include in that script outside that magnificPopup function
$('.custom-class').find('a').addClass('no-scroll');

PS: it will work – but with two buttons on that slider we had to find better selectors ! otherwise the second button will be triggered too.

as mentioned above give a custom-class in this case to the slider

function inline_popup_youtube_link() { 
?>
<script type="text/javascript">
(function($){
$(window).on('load', function () {  
	$('.custom-class').find('a[href*="youtube"]').addClass('no-scroll');
	$('.custom-class').magnificPopup({
		delegate: 'a[href*="youtube"]',
		type:'inline',
		midClick: true,
	});
 });   
})(jQuery);
</script>
<?php 
}
add_action('wp_footer', 'inline_popup_youtube_link', 9999);

PPS: because the link isn’t really a youtube link ( remember the link goes to that div with ID: #youtube-film )
if you like to use it on other places – the ID must have a string with “youtube” maybe you can name them #youtube-1, #youtube-2 etc.

OR choose as selector: for the anchor : a[href^="#"] ( replace it on both lines ) – it means the link starts with #
But then the second button in the slider must not be an anchor link of the page. This would also fall into the trigger.
________
Das dort die Vorschaubilder von Youtube gezeigt werden in einer lokalen Version ( daher meine Frage oben ) – wird bei dir nicht der Fall sein !
Es wird das Standard Borlabs Preview image gezeigt werden.
Da habe ich ordentlich borlabs und youtube kenntnisse mit eingebracht und eigene Scripte geschrieben.

Is it too complicated for you to implement?
maybe this is better – ( as mentioned above – the second button had to be not an anchor link leading to an id of a color-section or something like this )

function inline_popup_youtube_link() { 
?>
<script type="text/javascript">
(function($){
$(window).on('load', function () {  
	$('.custom-class').find('a[href^="#"]').addClass('no-scroll');
	$('.custom-class').magnificPopup({
		delegate: 'a[href^="#"]',
		type:'inline',
		midClick: true,
	});
 });   
})(jQuery);
</script>
<?php 
}
add_action('wp_footer', 'inline_popup_youtube_link', 9999);

Borlabs can block iframes – see : Borlabs – Content Blocker – Youtube :

This is the shorcode i put inside a div – and set for the div a class : mfp-hide
This class is the magnificPopup class that is set to display: none
With that code above – every anchor link that starts with “#” inside that custom-class ( you can have every other name for it ) will open in a lightbox. In this case it is that youtube film – blocked by borlabs cookie til you consent.
The button itself is linking to manual #youtube-film ( this had to correlate with the div ID that you like to open )

<div id="youtube-film" class="mfp-hide">[borlabs-cookie id="youtube" type="content-blocker"]<iframe width="100%" height="800" src="https://www.youtube-nocookie.com/embed/Uzjt3fvIlnY" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>[/borlabs-cookie]</div>

Must not have been so important after all.