This is user work on the machine itself.
Get UBU or MMtool for mcodes update
Get Intel ME11 tools package and latest FW 11.8
Perform a valid bios backup to preserve system data in case of system failure.
Follow the guides and post issues for help.
https://winraid.level1techs.com/t/discussion-ubu-tool-related-questions-reports-and-suggestions
https://winraid.level1techs.com/t/tool-guide-news-uefi-bios-updater-ubu
EDIT: Glad you made it, all it takes is a little of your time and a learning lesson from good readings.
There is no such thing as 'secure" and such paranoia can damage your brain.
The only thing that comes to my mind is a steel locker, buried int he ground as optional, and all plugs out, cheers 