The Updater on the Fairphone 2 didn’t like firewall Apps much, if I remember correctly. Perhaps it’s similar on the Fairphone 3.
It seems you are running NetGuard. Have you tried without the firewall being active?
There is no official way to download and install updates manually as of now.
If you want to do it inofficially, it could be possible, but this doesn’t seem to be exact science yet either. If you are feeling adventurous, you may want to unlock the bootloader of your phone (this includes a factory reset) and have a look into these topics …