Does anyone know why I can't play youtube videos in full screen mode on my server?

This is my server on DigitalOcean -

Ubuntu 20.04.3 Apache 2.4.41 PHP 7

The default youtube embed code doesn't work and I've tried several other embed methods but no luck. I've also tried another browser.. Still doesn't work.

For example I uploaded this codepen to my server -

https://codepen.io/fregante/pen/GgOvLM

I don't understand why full screen works on codepen but not on my server?

When I hover over the full screen button it says

Full screen is unavailable

Why is it unavailable?