It took me a very long time (more than a month since my last post), but I finally got it installed!
I needed help from tutorials and videos I found at droidwin.com
eg.
- How to Flash Android 15 Custom ROMs on Galaxy S20 FE - DroidWin
- How to Flash LineageOS 22 Android 15 on Galaxy S20 FE [4G/5G]
I used the vbmeta and orange fox recoveries recomended by @ronnz98
- Release Patched VBMeta · ata-kaner/r8q_archive · GitHub
- [UNOFFICIAL][RECOVERY] OrangeFox Recovery Project for S20 FE (Snap + Exynos) | XDA Forums
I do not really understand what I did, so the guides from DroidWin were priceless. Because of this I am not sure whether things not working are because of something I did wrong, or because of a failing in the ROM.
I will post about how I get along.
So far, the setup screens crashed every time I tried to enter a PIN. I tried several restarts and reinstalls before realising that I could skip this part. After setup was complete I still can not add any lock - pin, password, pattern or finger print - without the settings crashing. If someone knows of a way to fix this, I would be very grateful.
Thanks to @ronnz98 for the ROM and tips and to @aibd and @Xxpsilon for the advice.