Hi, I had same problem today. I was unable to connect to admin account using password.
A workaround I did was to edit Dolibarr "admin" account username to an already existing Cloudron username (using a Dolibarr account that had administrator rights). I could then connect with OIDC on the edited admin account.
But I'm pretty sure I was able to connect to that admin account with username/password months ago. I'm not a big fan of the workaround I used today.