Forcing everyone to use an approved OS is draconian.

I agree, but my point is that it wouldn’t be that easy to do either. I am hopeful that a system where servers take the OS’s word for it that you are in a certain age category would not smoothly transition into one where they also need proof that the owner of the hardware cannot decide that category, and that the system working this way would be accepted as a long-term status quo like those age selection menus were, because it would be actually a bit more effective at stopping kids who don’t know how to reinstall an OS so legislators could plausibly claim they did something without extra changes.