Welcome to the Roku Community!
We're sorry to hear about the issue you're running into. We understand that you having difficulties logging out of your Paramount + subscription.
Just to verify as mentioned by @RokuDanny-R, have you tried navigating to the bottom of the left-hand side menu to Settings > Sign Out?
To try to resolve the issue, we suggest removing the channel, restarting the device then adding the channel back again. Once the channel has been re-added, try to sign in with their channel provider and see if they are still experiencing an issue.
Please try doing this and see if it helps with what you're experiencing.