Blogger template can't play videos on fullscreen - iframe

Question

I bought this movie library template for Google Blogger, It uses this feature
"Big Screen Player" On every post, you have to need use below iframe player on HTML tab.
<iframe allowfullscreen="" frameborder="0" height="315" id="bigframe" src="https://www.youtube.com/embed/VIDEO-CODE" width="100%"></iframe>
but I can't use the fullscreen mode for youtube videos or google drive videos
what I'm missing?
I've try to contact the seller / developer but theres no anwser...
here it is all of his work:https://www.templatemark.com/search?&max-results=9
all templates this developer is selling have the same problem
here is the demo blogger frontend:
https://demotemplatemovie.blogspot.com/2021/07/test-post-1.html
please if you need access to the edit ask.
thank you very much

Answer 1

Use allow="fullscreen" inside the iframe tag. Or other tags you can use according to this answer are:
allowfullscreen
mozallowfullscreen
msallowfullscreen
oallowfullscreen
webkitallowfullscreen
Sample (You can try it somewhere else as Stack Overflow's compiler is facing issues playing it):
<iframe src="https://www.youtube.com/embed/XGk2EfbD_Ps" title="YouTube video player" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
UPDATE:
Add allowfullscreen in the var c of the jquery, such that:
$(function() {
if ($("#bigframe").length > 0) {
var a = $(".single-post-title").text();
$("#titlevid").text(a);
var b = $("#bigframe").attr("src");
var c = '<iframe src="' + b + '" id="covervideo" frameborder="0" allowfullscreen></iframe>';
$(c).appendTo("#myvideo");
$("#bigframe").remove();
} else $("#myvideo").remove();
});