I really think Chan Ho Yin should logically be a mutant. He's based off a character from the comics who is a mutant and his powers were
almost completely unexplained.
https://marvelcinematicuniverse.fandom.com/wiki/Scorch
Ray Johnson, who you may know as John Wraith from X-Men Origins: Wolverine, was referenced on WandaVision. He's a mutant character but we know nothing of him in the MCU.
https://marvelcinematicuniverse.fandom.com/wiki/Ray_Johnson
Of course, Sony's Spider-Man Universe has already introduced mutants into its continuity with Shriek. Madame Web is also a mutant. There's no reason to believe they aren't mutants so I'm assuming they are.
I really don't think we need a big explanation for mutants in the MCU. Just introducing them naturally like any other character is fine.