Okay, this is a bit embarassing finding the solution after just posting a help request :-) But I'll leave it here in case others f*** up like me
I booted into the backup-bios:
- pc i powered off
- booted by holding the powerbutton during boot, you then actually power it back off again because you are holding the button.
- pressed the powerbutton to boot it up again, but now you switched to the backupbios
- backup bios does some repairing magic on the main bios
Booted into main bios, loaded optimized defaults and was back into windows.
The secureboot watermark is still there but I think i'll just leave that there now :-)