The only mention/appearance of a toilet in the pokemon universe is in the Pokemon X/Y games, and in no other entry of the series, we have ever seen another toilet or mention of sewage system.
Does this mean people unironically shit in the streets in the Pokemon Universe?

It's already implied pokemon poop outside, but what about people? I've never seen a npc at least doing a reference to this, only to the former.

And no... Humans in the game eat and have bodily function as well as pokemons.

This leaves us with the safe assumption that people in the pokemon universe are filthy jeets and everyone poops in tall grass, lakes,etc...