Welcome to the forum. Is this an FP3 or FP3+ and can you confirm the update is the latest and did it happen immediately after the update or some time later?
So when did you do the update, have you not been able to use the phone since?
If it’s a faulty update the long story is to reinstall manually as it may have been corrupted on install.
First please start in safe mode if you can and see if that resolves the issue temporarily.
https://support.fairphone.com/hc/en-us/articles/360048843571-Safe-mode-for-FP3-FP3-
There’s always the reset option as a near last resort.