Hi,
I am using Bilberry theme - but maybe this problem is the same in other templates too.
When trying to show a video in portrait mode (from mobile phone) the video is always shown in landscape mode - visible is only upper half of the video.
What can I do to show the whole video in portrait mode?
The theme author’s youtube demo works fine for me on mobile regardless of orientation.
You can also test Hugo’s embedded youtube shortcode:
https://gohugo.io/shortcodes/youtube/#example
If you need additional assistance, I suggest you contact the theme author directly and provide some details (e.g., video page or shortcode, youtube or peertube or …).