Without seeing the logfile, it's difficult to say what the issue is, but my guess would be that you don't have
fof/oauth installed on your forum? This is an optional dependency, but was causing a boot error when not installed.
If that's the case, then updating 2FA to the latest version
1.0.4 will solve your issue, otherwise you can remove 2FA with this command:
composer remove ianm/twofactor
Please provide the error from your logfile if you'd like me to look into the problem further..