what country are you in??
Australia is the only country that banned the base game completely on Steam and can not be activated by key. But even in Australia the DLC can be activated by key
every other country can activate the base game and all DLC by key
Viewing post in Midnight Ride - DLC Season Pass comments
I am from germany. For games with sexual content the goverment of germany demand an age rating (18+) from Steam (so nobody under that age should buy this kind of games).
Steam hasn't any intrest in control everyone (for his age) so they do region block for nearly every game with sexual content since the beginning of 2021.I bought a few ganes with this content before but I can not buy, install or download any DLC because of this region block.