I use a secondary account that is attached to my YouTube account when watching YouTube. I just purchased a Roku TV and unlike my other Hisense android TV I cannot sign in. Some posts on here also highlight this issue but these seem to be using software that has a third sign in option that lets you authenticate via YouTube.com/activate solving the problem. My TV does not have this. I have the sign in by phone and sign in on TV options. Sign in on TV does not prompt for an account selection like my other TV does. Sign in on phone will automatically sign me into my primary Google YouTube account rather than the account I am currently signed into. Considering a return over this as this is key functionality that just does not exist on this TV.
Never mind what anything about the other Roku.
Highlight the App in Home press St*ar and remove the Channel.
If you have YoutubeTV nuke that also.
do a Settings/System/System restart
reinstall Youtube and log in preferably with a Gmail account.
It wont matter that youre signed in to other accounts elsewhere.
Sometimes having YoutubeTV alongside helps but dont at first.