On Linux you can just ignore the intel-ucode package (or whatever it's called) and not update your CPU microcode. BUT, I think they also have mitigations in the kernel, so you would have to not update your kernel, or somehow remove the patches.
The CPU microcode updates are also delivered through motherboard firmware updates, so you'd have to avoid those too. But some of the microcode updates permit more efficient mitigations, so unless you can completely avoid software updates with mitigations, you might actually want some of the microcode updates.
For most of the mitigations there are kernel parameters to disable them if you wish to do so