Yeah, such a standard could be great. But at this point I have no confidence in any governments pushing for that sort of thing. I would be ok with great parental controls. Government controls can fuck off.
Device makers doesn’t sound like operating system to me. Just need to make sure there is a distro that the device comes with which does this. So if you make ToBeReinstalledOS which only comes with an age checkbox and USB media creation tool to the bare minimum compliance required and no network drivers to prevent accidental age verification. Your device is compliant and can be sold in authoritarian countries.
Yeah, if its done in the form of optional parental controls I would be totally fine with some kind of OS level child flag that things can check.