As long as you’re using the “PlayerCapsule” prefab and the ground has a collider on it, that should all be good.
Perhaps there’s something wrong with your collision layers? I noticed that the first person character controller starter asset puts the player on layer 8 (which isn’t named by default, so I just named it “8”).
If that dropdown is empty, then you don’t have a name assigned for layer 8, and this shouldn’t be the problem, since every layer defaults to colliding with every other layer.
If it isn’t empty, check the Physics section of the project settings. If that layer doesn’t collide with Default (or whatever layer the ground is on, which you’ll want to check!), you’ll fall through the floor