Rounded corners are the after-the-strategic-decision legal justification.
This is no longer possible on any phone, tablet, or computer Apple sells: all require online activation with device-specific info. There is no way to put the device back into a known state offline or without Apple having an opportunity to tamper with it (or be forced to tamper with it).
It is still possible on all of their computers, just not their phones or tablets. Intel Macs (which are still being sold in large numbers) can always be wiped and restored from USB without an internet connection, and Apple Silicon Macs can do it if you set the boot-loader to "Reduced Security" mode.
I would love to be wrong about this.
This is the case even if you have a full offline boot/restore USB.
I have a post coming out today about just this, and how it renders all current macs unsuitable for long term offline/airgap applications.
For some reason this ridiculous restriction reminds me when Apple sued Samsung because their phones had round corners.