appendTo vs. self-closing tag jquery >= 3.5

[santaclaus21]

Code:
$('<div class="popup" data-popup="iframe-1">' + '<div class="popup-flex">' + '<div class="popup-inner">' + '<iframe src="'+url+'" frameborder="0" height="100%" width="100%" />' + '<a class="popup-close" data-popup-close="iframe-1" href="#">&#10005;</a>' + '</div></div></div>').appendTo('body').fadeIn(600);

After this code there is nothing after appended iframe:

It was working fine before JQuery 3.5. But, if I replace self-closing iframe to <iframe....></iframe>, everything is working as expected:

$('<div class="popup" data-popup="iframe-1">' + '<div class="popup-flex">' + '<div class="popup-inner">' + '<iframe src="'+url+'" frameborder="0" height="100%" width="100%"></iframe>' + '<a class="popup-close" data-popup-close="iframe-1" href="#">&#10005;</a>' + '</div></div></div>').appendTo('body').fadeIn(600);

Result:

And now, code after iframe is not lost. Why ? I couldn't find any important notice in Jquery docs / appendTo.

[mgol]

Please read the issue template, it provides this issue as a frequently reported one. This is covered by the jQuery 3.5.0 blog post & the upgrade guide. Also, it's a duplicate of #4681, #4693, #4709, #4710, #4720, #4721, #4780 & #4823.