> if I understood it correctly, pre-2023 devices don't receive OS updates.

Indeed. An ancient 3-year-old device isn't receiving any OS updates. Which means it doesn't get features, its core software isn't updated inculding such minor things as the browser (most apps on TVs are browser apps), store etc.

Eventually its certificates will expire and it won't be able to connect to most things

> How long should support for devices last in that case? And what should be supported?

Depends on device. People don't buy TVs every year. So a 10-year support isn't out of the question. That said, 10 years should probably be minimum for almost all hardware.

E.g. Microsoft supports Windows for ~10 years, and for a much wider array of hardware.

After that: open up, and let people do whatever they want with it.