Are fabric shower curtains actually machine washable?

Yes — that's the main reason r/BuyItForLife and r/ZeroWaste threads recommend them over disposable plastic. Most 100% polyester and waffle-weave curtains can be washed on cold or warm with regular detergent, sometimes with a splash of vinegar or bleach, and air-dried on the rod. Linen-blend curtains usually want a gentle cycle and a mesh laundry bag.