The same is happening to me but on version 1.77.100
I even went as far as doing what mpql suggested trying here: Twitch no longer supports Brave - Browser Support - Brave Community
Also, I cleared all history/cache/cookies then restarted PC and ensured no VPN was active.
I can login through Microsoft Edge since it is a chromium derivitive but not Brave. Could they be singling out Brave or something? (I don’t know) but I wanted to chime in to state it isn’t just Sekyno having this problem. @fanboynz