This is also happening to me. I tried creating a new API token, which I’m able to login with using forge login. But still no luck with forge install --upgrade. I’m able to run forge deploy just fine…
Forge is great in theory but these random regressions that pop up really make you want to pull your hair out…
After contacting the support, I managed to solve the issue by manually upgrading the app from the admin page (manage app). But yeah, I’m still facing that issue until now