Yes fair enough, but linking us to other threads to understand your situation also leads to confusion. The thread you referred us to is titled “Restoring stock OS after unsuccessful iodé install” and there is so much back and forth on it about if FRP is enabled or not and try this try that etc that it leads to a bit of confusion.
Now back to your case: I will check with the devs to see if they can comment on how to reset the FRP trigger (that I am still not certain if that is the reason you can’t enable “Allow OEM Unlocking”).
Note I am not a dev at that level btw and yes I have never dealt with FRP getting triggered or even realizing it was a think until recently… I still don’t find it to be a particularly useful design feature if simply flashing another ROM would reset FRP protection.
Note that the other Fairphone user who had FRP triggered did reset it by using the Fairphone web installer but in their case their first sign of a problem was that they could not disable OEM Unlocking. After install of iodé, that option “Allow OEM Unlocking” should remain enabled, so did you then disable it yourself, and after that it was not able to be re-enabled again? Or how did it get disabled? It seems that triggering FRP doesn’t remove that option, as again this other user that triggered FRP did not have that happen?
My suggestion while we see if the dev team can advise on resetting FRP while the device is locked is to attempt to upgrade to iodé 7 beta. I am hopeful that would fix the issue and re-enable “Allow OEM Unlocking”, after which you should be cleared to reinstall FPOS which should reset FRP. At least it is worth a try?