@yvmuell Ok thanks
@AlphaElwedritsch
So an other question, let’s say I take the risk and that the “get_unlock_ability=0”, would it be possible via a simple firmware update to solve this? If not, the phone would be unlocked forever 
Ok so for your IodéOS =>
" If you get 1, everything is fine.
Then start again, beginning at Step 8)
1. remove SIM card and check that akku has at least 50%
2. eneable USB Debugging and “Allow unlock OEM” in Developer Options
3. check if adb is working and device is recognized correctly =>adb devices => ACK USB debugging on phone-screen. check box: always trust
4. adb reboot bootloader
5. check if fastboot is working and device is recognized correctly =>fastboot devices
6. fastboot flashing unlock => Acknowledge unlocking on phone (VOLUME UP + POWER) Device is doing a factory reset and reboots to system
7. start again in bootloader => switch phone off. pull out USB cable. press Volume (-) and put in USB cable in. Keep Volume (-) pressed. Phone should start in bootloader. (¹)
8. check if fastboot is working and device is recognized correctly =>fastboot devices
9. fastboot flash recovery_a iode-3.0-20220530-FP4-recovery.img
10. fastboot flash recovery_b iode-3.0-20220530-FP4-recovery.img
11. fastboot erase avb_custom_key
12. fastboot flash avb_custom_key avb_custom_key-FP4.bin
13. press VOLUME UP until see message reboot in recovery. Then POWER
14. From recovery => Factory reset => Format Data/factory reset
15. From recovery => Apply update => Apply from ADB =>adb sideload iode-3.0-20220530-FP4.zip
16. back to bootloader mode. From recovery => Advanced => reboot to bootloader
17. check if bootloader unlock ability is possible =>fastboot flashing get_unlock_ability → (bootloader) get_unlock_ability: 1 ==> if you get 1 then follow with step 18) otherwise do not lock bootloader (can brick your phone) and follow with step 19)
18. fastboot flashing lock
19. reboot system. First should see a Lineage screen doing a wipe. After a second (automatic) boot you should see the yellow boot screen and then the iode bootscreen.
20. start setup wizard
(¹) From FP Support Page:
Alternatively, you can disconnect the USB cable, turn off your Fairphone, then connect the cable and hold the volume down button. After a few seconds, you’ll see the fastboot mode"
ps: for your instructions back to stockOS, did you use the procedure given by fairphone?