How can I easily make separate mesh joints limbs that blend well together like Rthro limbs?

I’m trying to learn Blender, and I’ve noticed this in many other Roblox games and in the Rthro sets, there’s like a roundish smooth end to the limbs so that when limbs move, it looks more natural. I was wondering how I could replicate this effect, and if I could separate preexisting meshes and models, and replicate this effect instead of having to do it manually.

I dont really know how to help you but you can read this post it explains it Skinned MeshParts are live!