California's law explicitly requires the system and apps to take the user's word for it and not use other information to determine age, which more and more feels to me like kind of a brilliant move to cut the legs out from under other attempts to use the same for surveillance while still satisfying all the surface-level "protect children" sound bites.

So, Linus? Patrick Volkerding? I mean, I can build a Linux system from basically nothing.

Hé man I thought us Europeans were kings of dreadful regulations!

For what it's worth, the "verification" in the California law (not a bill, it's already passed and takes effect 2027) is basically the Steam birthdate popup interstitial. There's explicitly no actual link to any outside information, just requiring that the system save a value the user sets and then that apps use that value for any age gating.