The government could send an order to the software developer to patch out that turning completeness, and ban the software if it's not complied.
I get what you mean, it's never possible to 100% limit things. But if you limit things 98% so that the general public does not have access that's more than enough for authoritarian purposes.
Theoretically, you can have a totally owned device managed by Big Brother, yet generate AI smut with a general purpose CPU built in PowerPoint.
How do you possibly regulate that?