Many major operating system updates to computers of mobile phones are also "opt in" while not providing a way of downgrading—granted in the case of computers you can often "just" reinstall from scratch, possibly factory reset in many mobile phones has achieve the same?

Granted Tesla is pretty naggy about the updates should you choose to hold off. But as far as I know, it's not limiting any functionality should you choose to do that.

For example the Polar watch app simply says you need to update the app firmware to keep using the app: that's not opt-in.