It's certainly not had a lot of development over the past couple of years but I think that's partly for two reasons:
- RealityKit has clearly been a priority due to the Vision Pro.
- SceneKit is already fairly mature and works well - although some things are fiddly.
SceneKit has a scene graph, PBR works, there are hooks for post processing (SCNTechnique), there is a way to overwrite rendering for an an object (SCNProgram or snippets) so you can basically do anything you want - but you need to be fairly experienced in rendering tech if you want to go out of the realm of the editor.
I use SceneKit all the time for hobbies and it works really well - docs could be a lot better but there is stuff out there.
SceneKit does not provide any VR/AR functionality so if that's a use case you can scrub it from your options.