I think in that case it makes sense to knock but in most cases if I see a single use bathrooms with the little occupied in red or vacant in green lock indicator on it I’m just gonna assume it’s free if it’s not locked and open it. I haven’t been burned by that yet because in most situations people will lock them when using them.
You can still get that by just playing very small indie games. There’s tons of small games out there being made by just a handful or even one person that have these kinds of little fun things scattered throughout them. They are harder to find by their nature but that culture is still very much alive in the indie space.