[wtallis]

There are workarounds for downgrading microcode, because the CPU itself doesn't actually have non-volatile storage for microcode updates and relies on the motherboard firmware to upload updates on each boot (and motherboard firmware can often be downgraded, possibly after changing a setting to allow that).

Which is probably why Intel has changed to disabling AVX512 using fuses in more recently manufactured Alder Lake CPUs.

[monocasa]

My point with "a lot of newer systems" was that there are motherboards now that completely lack a version of their firmware with the microcode that allows avx-512. There's nothing to downgrade to without an exploit to allow making your own firmware images with mixed and matched components.