FD is most often readable, but nor writeable, and ME is often locked for reading and writing, yes.
ME version got updated from 20 to 23, but 23 is same as 26. If a vendor bios update overwrites the ME and under which conditions isn’t reproducable. But I did check the ME configuration and there’s no change in settings for all 3 versions.
So it’d interesting if cleaning the ME of your defect spi would solve the problem. A CH341 is cheap and always ‘nice to have’, you got a socketed chip, so it’d be easy and risk free.
ME cleaning guide:
https://winraid.level1techs.com/t/guide-clean-dumped-intel-engine-cs-me-cs-txe-regions-with-data-initialization/