Upgraded last night and login button no longer works

[Falco]

You have a misconfigured SSO, disable with:

Official Single-Sign-On for Discourse (sso)

What if you check it by mistake?

If you check enable_sso by mistake and need to revert to the original state and no longer have access to the admin panel, visit /users/admin-login and follow the instructions.

OR, from server console run:

cd /var/discourse
./launcher enter app
rails c
irb > SiteSetting.enable_sso = false
irb > SiteSetting.enable_local_logins = true
irb > exit
exit