some opensource game engines progressed nicely

openTomb seems to be playable now.

https://opentomb.github.io/

It is engine for a Tomb Raider 1 - 5 games.

Remedy entertaintment first game Deat Rally, open source remake.

http://dreerally.com/

Redneck Rampage is actively developed. Actually RNR is based Build engine and there are lots of open source build engine game project wich has advanced nicely.

https://gitlab.com/m210/RedneckGDX
https://www.blood-wiki.org/index.php/NBlood

Diablo is progressed nicely, is there already port of it for Amiga OS4?

https://github.com/diasurgical/devilution

Need for Speed would be another nice to have, as there is not many car games and this should be low specced enough.

https://github.com/OpenNFS/OpenNFS

There is also a open source reimplementation of Escape of Golditz. It is marked as a completed.

https://aperture-software.github.io/colditz-escape/

Dungeon keeper was/is one of my favorites. KeeprFX is playable opensource remake. Requires original game files.

https://lubiki.keeperklan.com/html/dk_keeperfx_dwnld.php