I agree, Godot's 3D tutorials have certainly not been plentiful. I think it mainly has to do with previous versions (pre-dating 3.0) - the 3D renderer just wasn't very spectacular, and so most people used it for 2D games - thus, that's what tutorials focused on.
However, lots of tutorials have been popping up recently, and I have a feeling even more will down the road. Thankfully, GDscript is easy to grasp in 2D, and easy enough to "port" to 3D.
I might try and port my current project from Unity into Godot (it's 3D, hence why I wasn't using Godot from the start), and see if I can't learn how to get it all working in there. I think the best way to learn it for now, as you said, is to just keep experimenting.