Or legislate that unsupported software becomes public domain or is open for development and the public can try and make the updates themselves.

Forcing people to upgrade entirely depends on the nature of the upgrades and the motive of the company. What we need is competition so there are alternatives for people to use if they don't want to upgrade. But somehow Microsoft is not considered the monopoly of the PC OS market, despite being a monopoly, and uses that position to force changes nobody wants but them, like turning window into an AI data farming scheme that violates user privacy.