Then they are out of luck with this new T4 security chip cutoff, Apple says that it cuts off the mic when the laptop is closed, and there's no way even the kernel can override it:

“This disconnect is implemented in hardware alone, and therefore prevents any software, even with root or kernel privileges in macOS, and even the software on the T2 chip, from engaging the microphone when the lid is closed,” said the support guide.

So in this respect, there's no difference between the T2 chip cutoff and a physical switch... except that there could still be a backdoor in the T2 chip cutoff that Apple hasn't admitted to.