Apple ID: Enter the password for "".

Some days ago I got the notification on my iPhone11Pro to "Update Apple ID" since the company I'm working for claimed their email domain. I had been using my work email address as Apple ID for years, but decided to go along and simply switch to using a @icloud.com email address as Apple ID.

I initiated the switch on my iPhone until realizing that I couldn't create the new @icloud.com email right there and then. So instead I switch to my computer, logged into iCloud, created the icloud email address and performed the Apple ID switch there. It worked fine for iCloud and also in AppStore on my iPhone.

BUT then I realized that I could no longer access my Apple ID settings on the iPhone, since it now thinks my Apple ID is "" (and there seems to be no way to enter it anywhere). I also cannot SignOut of my Apple ID since I would need to first turn off FindMyPhone which requires me to enter my Apple ID Password for "" ... argghhh!!!

Is there any way to tell my iPhone that I am not Apple ID ""?

Maybe reset to factory settings, enter the correct Apple ID and then restore all my content from iCloud?

(I'm afraid to try this since it might start asking me to enter password for "" there too).

Thanks for any hint on how to fix this!

-Tom