I remember I saw somewhere on the internet a way to use url modifiers to set mobile version of YouTube permanently - until the current tab with that url is closed.
I tried searching here, but don't see anything similar.
It was something like
https://youtube.com/?app_force_m=1
or https://youtube.com/?mobile_force
or https://youtube.com/?force_version=mobile_app
Trying to use my intuition, but too hard.
To get the mobile version use: https://m.youtube.com/?persist_app=1&app=m
Or perhaps you want a direct embed of the video? https://www.youtube.com/embed/dX3k_QDnzHE