So, Macs are clearly vulnerable. The CIA have shown us that. Intel made a tool, which I looked at briefly....it doesn't seem to be an easy thing to use for the average end-user....
https://www.pcworld.com/article/3179348/security/after-cia-leak-intel-security-r eleases-detection-tool-for-efi-rootkits.…
If you Google Mac and rootkit, you'll find a number of hits concerning CIA activity, as well as what a couple of researchers showed at industry conferences (one was called Thunderstrike, I think, and then there was a more concerning sequel to that one).
It's not a safe world. Apple's, or anyone else's, contention that Macs are malware proof is laughable.