If you look at <https://github.com/unknown-horizons/> you will see this message:
Unknown-Horizons based on Fifengine is no longer in development. We are porting it to Godot Engine.
Please dont report any new bugs.
Only bugfixes will get acepted for maybe an last release.
New git repo for the Godot port is: https://github.com/unknown-horizons/godot-port
That's all I know. But I thought it was worth to mention it here.