This is in the comments below: It's sometimes pronounced "max", so it sounds like they is named "Max Somelastname". It is sometimes pronounced "mix", which opens up a non-binary person to unpleasant jokes which write themselves. It is sometimes pronounced "mex", which in the U.S.A. sounds like a racial slur. And the people who pronounce it the different ways all insist that their way is the correct way - and who's to argue with them, since "Mx" has no vowel?
Pronouncing it "Mox" avoids all those issues, so of course no one pronounces it "mox". Or spells it Mox. That would be too easy and too clear.