Rigidbodys, arent really made for custom physics, I suggest using characterbody. You could also try changing your rigidbody mode to character, I dont know if it still works in godot 4

You could hide the arms but still project their shadow ig? Not sure I actually understood the problem, sorry

It worked perfectly. After a little tweaking my squishy little slime is bouncing all around. squish.gif

Unfurtunally godot dont have a good physic system for cars...
There is a guy that is building a new one using gdscript : https://www.youtube.com/watch?v=6hEL66P1WQw
In general, if you need very realistic physics, you will need to build something similar, and its quite complicated.