There is some nuance to the language, and there might be litigation to follow; but age attestation and age verification are wildly different things:
Age attestation is just providing a birthday, like many sites such as steam, require before accessing most games. There's nothing stopping a 10-year-old from claiming to be 30.
Age verification, though, will be more of a legal process: requiring government documentation, biometrics, ai data harvesting, tracking, etc. and will result in the OS theoretically being required to keep your specific pii to provide to downstream consumers of this data.
Those of us who grew up in the age of the early Internet have 'handles' or 'usernames'. Those that grew up in the later Facebook age use their real names. Us elders see this tying of identity to computation as an invasion of privacy.
I've had this handle for decades across multiple platforms. I've probably identified myself, but you would need to put in at least some work to figure out what human being I am. We call that doxxing right now, and it's generally seen as hostile. This bill eradicates even that layer of defense by requiring my computer to know who I am, and sharing that data with Meta, Google, Facebook, Lemmy, etc. effectively my computer will doxx me.
While the intermediate result is not that my privacy is instantly compromised, anyone with a clue can see the future here: if the OS knows who you are because of this law, then the browser can know who you are, and the website can know who you are and when you say things the government doesn't like, you can be... Removed.
This is what we call a chilling effect. And that is also generally understood to be bad.
This bill, and all others like it, are bad.
Edit: And if this bill is defeated, there will be others. This is not going to end, and each version will be an existential threat to privacy.