How do you make space engineers type mining?

I don’t want it to be exactly like it, but here is what I want to happen: A projectile with a rigid body collides with a rigid body cube or mesh. I want that cube or mesh to have a “dent” in it, perhaps depending on the size or the mass of the projectile. I also want the cube or mesh to fully disappear if it get’s too many dents in it.

Your looking for Mesh Deformation. If you want a turnish key solution, there is a free asset available in the store:

Meshinator

Also if you search google for Unity Mesh Deformation, you will find lots of information.