@lennybacon @lenaschimmel @uint8_t @fragdenstaat finally tried via #eID which creates a new account (though the text sometimes states different implying you can link it to your existing account) leading to another login failure if you're logged in with your "old" account.
And finally, #eID login works, and I can proceed.
The form is somewhat strange it seems to be made for businesses and orgs, I have to provide an org name etc. I wrote "private person" 😅