I last updated the app Yesterday on my Sony TV.

Playlist, History, and Channels are all plain black today, Subscriptions says "Oops. Can't load content. Try to login again via settings".

I updated the app again just now (to Beta 12.41), and it's still saying the same thing. I rebooted my TV - same problem.
Running the real Youtube app still works OK (subscriptions etc show properly).

I still have the old "Smart Youtube TV" app installed as well - web_20210829_10_RC00 - which is a curious version, since I've not updated that since I installed more than a month ago. It's still showing all my subscriptions etc fine (although playing ads)

Something internally must be broken with the latest version(s).

Additionally - I created a new youtube account and logged in to that - same problem as above (the "Oops." error).
Note that the error says "Try to login again via settings" - but there is no way in the settings I can see to do that (this is also a new account, so it's clearly not a login problem really).

I also did, in the "Settings" under "Accounts", the option "Select on boot" - so when I start the app, I can now select one of the 2 accounts I've got each time - presumably this will "log in" to that - but it's still showing black-screens for Playlist, History, and Channels and "Oops" on subscriptions every time for both accounts.