“Basically, Apple decided to break the ARM spec by removing a mandatory feature, because they figured they’d never need to use that feature for macOS.”
Any two processes on an M1 can pass data through a CPU register nobody is supposed to touch. The finder says it’s harmless, and he’s right. A covert channel only helps once you are already compromised. The real story is the FAQ, where Apple’s spec-breaking shortcut makes the fix far harder for every OS that isn’t macOS.