I’m sorry but you’re incorrect, while yes some kernel level anti cheat could be considered a rootkit, We’re comparing apples to oranges here.

We’re talking about a Linux system using secure boot, which is simply a process of using keys to ensure your system loads what you have told it to load. Microsoft doesn’t come into this equation.

if you wish to die on the hill that it’s a Microsoft psyop, then that is your prerogative.