https://wiki.unrealengine.com/Compiling_For_Linux#Additional_Step_for_Linux-ARM_platforms
Unreal engine and the scripts you write are in C++ and it can build to linux arm platforms, so would that be a viable option to make games for the Librem? I use visual studio with Unity, though I don’t mind learning a different programming language if that means I can use a scene view such as Unity or Unreal has. Especially for games I really like being able to rearrange things and creating objects in a scene view and then attaching scripts to them.
If Unreal is a good option then I can start messing around and learning C++ and the engine, and test anything I might have made on the phone when it ships:)