While playing with youtube embeds in joomla, I noticed sadly by default they go by fixed size and do not adjust with the rest of the responsive template. As a result commonly the videos are clipped on phone resolutions. If one tries to set the width and height to % based, then for whatever reason the max height is 150, which usually is not what you want.
As a side note, for those new to embeds, one has to turn off the iframe filtering in their article editor settings, the default being tinymce.
Anyway, this article gave some useful tips that worked for me: https://css-tricks.com/fluid-width-video/
This one also worked, which appears even more simple: https://ontargetwebdesign.net/tutorials-joomla-editing-worpress-jce-editor-html-start-100/161-make-a-youtube-video-responsive.html
But it is still a hassle to go back and add formatting manually. Is this still the situation with Joomla4, and perhaps Joomlart has considered making an extension that could add the responsive toggle to adding video embeds? I think it would be popular and development should be relatively easy.