It’s best not to. Leaving your bar on the floor exposes it to dirt and dust, and this can cause issues in the bar sleeves.
You shouldn’t leave them propped up on an angle either—you want to minimise force on the bushings or bearings when they’re not being used. Essentially, barbells are very good at temporarily holding a lot of weight, but they’re not designed to handle sustained force from other directions. This is also why you should never store them with the weight plates left on.