Theme Horse

Yes you have to manually edit the video as HTML through ‘edit as HTML’ option as should wrap the iframe that you get on video element because the classic editor has not control for video to resize the video size or you have to add the video of smaller in size.
If you don’t want to work it manually every time then it’s better to upgrade the WordPress to latest version where you can edit the page content through block features and you can easily add videos that automatically responsibly.

Thanks