Right, I forgot that your get_unlock_ability is 0, and that’s needed for unlock_critical as well… It’s a weird state to be in 
If we go by the Fairphone instructions they first unlock OEM and then perform flashing unlock followed by flashing unlock_critical, which works because get_unlock_ability is only reset on first boot, so it stays on 1 during those reboots and the commands work.
However, since your bootloader is already unlocked, the OEM unlocking switch is greyed out in the settings, so we can’t just get it enabled again.
Check if you can toggle OEM unlocking in the developer options, if it’s greyed out we’ll have to take the Magisk route to make it toggleable again.
If that’s the case and I’m not back to the forum in the next few hours and you get bored, here are the (very old) instructions for the Magisk route:
You’ll need a patched root-enabled boot.img, so after the first step transfer the boot.img from your extracted factory images to your phone, open the Magisk app and patch it, transfer the patched one back to your PC and continue the next step with that image.