that's why you turn on Lockdown Mode or swap to Linux completely :)
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Linux will get there, but currently macOS is much more secure as a desktop.
Such a hardware backdoor is rather more severe than most of what has ever been discovered on non-Apple devices.
As long as the main protection of the Apple devices consists mostly in their lack of detailed technical documentation, one can never know whether other such hardware backdoors exist.
Good security is layered. For example, even with a sandbox escape, and app could not read your full Documents directory, modify the OS, or install a firmware-level rootkit.