Hello there, my problem is that when the sphere game object is over the terrain, it falls, but the cube does not.
is rigidbody enabled?
if so click or just select the sphere and scroll down on the inspector you should find something called rigidbody remove it or go to constraints and press “freeze position” and select Y axis.
Or even box/sphere/cylinder collider… You need that to keep your character unable to fall through the plane/floor.