They can publish it as WIP/private/in-dev/not-entirely-pubic for 1 month on Itch/EGS/Steam, and then take it down after their client has seen it. Point being that it's not "very easy" to figure this out, as the individuals that want to skirt this rule will find a way that ticks the boxes but doesn't satisfy the intent.

Steam sells software and soundtracks, and previously sold movies. Epic sells developer asset packs. itch.io is even less discerning. I don't think that metrics holds well for determining what is a game.