I know that there already are several posts about this but i stil can’t solve the problem.
Colliders.
No Triggers.
Make sure you have as rigidbody and a collider for your sphere and a collider for the ground or whatever you are trying to collide with. Also if your sphere is way too small and falling way too fast it might go through things, although IDK if the new versions have fixed that or not but I remember that being a problem in 2.6.
Are you using a plane as your ground collider? I remember spheres falling through planes when they were both perfectly aligned at x=0, z=0.