What do you… mean? Is this in editor or in game? If in editor, use the Grid Snap that’s near the center of the Scene2D edit bar at the top just in the scene editor and customize from dotted menu.
I mean: 3d editor top header : [Transform] → Snap Object to floor
AS far as I know:
create StaticBody3D With CollisionShape3D can Fix that.
So No specific floor obejct can Create And it’s wired desctript confusing the novice user.