This is more a solution than a question, as I fixed the hanging youtube plugin.
So, in case you updated your Vero4k+ to 2021.08-1 from 2020.10, and the youtube plugin is totally hanging the Vero so you could see nothing but black screen and could not exit from this black screen.
I did the next: I opened the plugins browser, found youtube, went to settings of the youtube plugin, and in MPEG-DASH I unticked the “Use MPEG-DASH”, and then I rebooted Vero.
After it boots up I was able to play videos that were hanging.
Also, when I re-checked the youtube plugin settings, I noticed that MPEG-DASH was enabled again automatically.
Might be some issue with an upgrade and enabled-already MPEG-DASH state.