Family Sharing is a feature that developers may opt their games out of for technical or other reasons at any time.
Ubisoft, EA, and Rockstar running to opt out every one of their games.
Kudos to Valve, but for us remember as a general rule that if they have their own launcher, they have no interest in sharing.
opt out was already possible with the old system, and most devs didn’t opt out
Even Fall Guys only did it because Cheaters running rampant with family share.