Hi Andi,
in the documentation I can see this line:
If you set 'forwardClearPass' to 1 the backend expects the database to do the crypting. It will forward the clear text password to the database. Be aware of the security risk.
I understood this as that purely the encryption is done by the sql backend, not the password check. But as I am not a MySQL expert I might have misunderstood. But even then, it is impossible that my mysql backend would give back a ok towards the dokuwiki frontend as I don't even know how I would have done that. So I'm still not sure where this went wrong, as I see it access would have never been allowed as the passwords were wrong.
But again, I'm no mysql expert so I am sure I did a lot wrong. Really happy to have this working.