Skin Weight Painting can be very slow, especially if someone forgets to toggle of smooth mesh by subdivision
But I my case I didn't have that enabled, I do have a dense mesh to work with Spring Joints, problem remains is that it's too slow and freezes and crashes often (AMD 16 Core 32 Thread at 5Ghz & 128 GB host ram and a RTX 4090 graphics.)

I have set the shader to minimal mode, isolated the mesh and it still wasn't enough. So I thought, hey I can hide more than half the mesh with Edit mesh, then go back into skin weight editor.. as soon as did that and toggled off joints, the mesh are I tried to hide came back. Not only did that not work, trying to toggle the Bone display in the skin weight editor or the Bone tab failed to restore the rendering of the bone hierarchy.

So I found out how to restore the bone display. i had disabled my character and all other mesh parts to lighten the scene but apparently it needs the body to display the bones. i hope you find a way around this issue to work on weights, maybe as the user presses the button to paint, isolation mode helps to show only the area your painting plus extra little extra that could be set with a radial render area slider for Real-time GPU Isolate.