Hi Martin,
There is currently an issue with creating new accounts via social idP. We do have an internal query on this and it’s being investigated. The cause is due to the auto-enabling of the feature that requires MFA for access to the Admin Dash, and with social idP you aren’t prompted to set up a second factor. This only happens with social idP at this time.
I’m going to DM you to request some details for verification and then I can toggle that feature off on the org and then you’ll be able to get in.