If you have a backup of all your important data (pictures, contacts, messages, etc.) or if you are ready to set up your phone again without a backup, you could try the following …
- Boot the phone into dic:recoverymode (<- really read this on how to navigate there with the buttons)
- Run “Wipe data/factory reset”
- Run “Wipe cache partition”
- Run “Reboot system now”
I’m not quite following … are you referring to this post?
In the end, if you believe the OS could somehow be damaged, here’s how to wipe the entire Fairphone 2 and install it from scratch, just use the manual installation file for the older OS in the process … (for English, you can translate the text at DeepL, it’s pretty accurate, I checked) …