When you “claim” the prize it will be a “steam key”.

Anyone can then use that “steam key” to add that game.

So what is normally done is someone creates a post saying the name of the game and you have a free steam key to give away, and whoever replies first, DM them the code.

On reddit there were bots that scrapped codes

On Lemmy you might be able to just post it, but whoever redeems it first gets to keep it.