I recently acquired a set of AirPods Max after something like six years of using Beats3 OTE headphones. They sound fantastic, and, as with any Apple product, they work seamlessly with the rest of my Apple crap.
One day in the last week or so, the buttons on my AirPods Max stopped working. It also stopped giving me the familiar “bong” when I put them on (all other AirPods models do this, too). I tried restarting them and resetting them. Everything I could think of, but nothing worked.
I was about to schedule a visit with the Apple store so they could either fix or replace them, but I was lucky enough to discover this Reddit thread that gave me the answer.
While removing my headphones a few days ago, I inadvertently removed one of the ear cups (I didn’t know they easily detached before doing this). It turns out that when I reattached the ear cup, I put it on upside down. They really don’t make it obvious that there’s a correct way to attach the ear cups.
Just now, I took it off, rotated it 180 degrees, and put it back on. And the buttons began to work like magic.
TL;DR: If your AirPods Max buttons don’t work and you’ve tried resetting/restarting them, try removing each ear cup and rotating it 180 degrees, then re-attach.