Social media sites are going to get in trouble if they can't verify ages, and they want the age information so that they can sell it to advertisers. Microsoft, Apple, and Google are going to create APIs that the various services are going to trust. If your alternative implementation of the API response isn't signed by a key controlled by Microsoft, Apple, or Google it will be blocked outright. This loophole is not a victory, it is a huge defeat.
These operations can get in actual legal trouble if they don't gather this information. Plus, it is in their best interests financially to gather this information. Verified age information is ridiculously valuable to them. They want to be able to get your verified age, and now they have a legal reason to require it. Plus, every bot, actual predator, and other bad actor is going to try and climb through this Free Software exemption. The overwhelming majority of traffic that can't provide a response signed with a key by Microsoft, Apple, or Google is going to be crap, pure and simple. This law doesn't say anything about requiring that the service work with Free Software. Instead it puts Free Software in its own little ghetto. One thing is certain about ghettos, they don't put you in a ghetto for any reason but to be able to discriminate against you.
It is far more likely that a year from now Linux will be unusable for sites that require age verification, than it is that Linux will be the loophole that websites allow ti work despite not having "certified" age verification. Microsoft, Apple, and Google didn't fight this because they know that this actually strengthens their grip on operating systems. From now on, any device created by people that want to potentially do business in California (ie, everyone), is going to have to find a way to get a "blessed" age verification API by one of the big three. If they can't get that blessing then their fancy new device is unlikely to work on any service that has personalized accounts.