@TeamYouTube 3/2 update: i can sign in MANUALLY via Incognito tab, but the SIGN IN button on YT automatically tries to log me in to my current Google account; i can't force the SIGN IN page to allow me to input email/password manually, otherwise i could log in just fine.
Have you tried signing in to a different device? Or restarting your browser? If you’re still having trouble, these tips may help you through the process: https://yt.be/help/KyrL . Let me know if it works.