Probably, at least until someone successfully gets a court to say otherwise, by which time it'll be irrelevant because everyone will either have installed & enabled it to get the updates or (less likely given how entrenched many iDevice users have become) moved to other products.
And after the case to stop them refusing security updates for those without it installed+enabled, there will need to be another one to force them to allow it to be disabled, then a few circuits around the court of public tattle to make it really disable and not magically re-enable itself at random intervals.
Interestingly, iOS 15 is the first version of iOS in history to be optional if you want security updates. You will be able to choose if you want to go to iOS 15 and get the new features (including the CSAM prevention stuff), or you can stay on a security update only channel for iOS 14 (for a unknown period, but I'd guess until WWDC 2022? N-1 seems reasonable).
And after the case to stop them refusing security updates for those without it installed+enabled, there will need to be another one to force them to allow it to be disabled, then a few circuits around the court of public tattle to make it really disable and not magically re-enable itself at random intervals.