Godot is currently used as the 3D engine in the Tesla in-car UI, possibly also in their apps (?). It's cross platform and open source and has a pretty vibrant dev community.
It's reasonably modular and you get access to the full source, so if you wanted to drop many chunks of it that aren't relevant to you, you could, in theory. Of course it's still a 20M+ LOC codebase and all future version updates integration are going to suck big time, but a large enough team can likely power through the suffering here.
