Yes, the intel management engine is the very definition of a backdoor. See www.techrepublic.com/article/is-the-intel-management-engine-a-backdoor/
There was an insider geek who worked on the ME said it is bad news and has total access to your system.
What's the threat vector? What if bad guys told your system to wipe all your files? To alter the BIOS so that it's unusable? Or simply to report back to mothership if you have certain keywords in your recent files like qanon, crisis, storm, comey, etc.
This anon suggests disabling manufacturer and intel updates to your system, thus limiting the degree to which new/worse software could enter/crack/ruin your system. A geek more paranoid than I backs up his system by pulling a mirror (there's that word!) drive of his online system to pop in his offline system which is kept mostly powered down.
Also a secondary firewall with egress filters so that your system talks only to the systems you explicitly permit.