Steps I use to update firmware:
1. Plug in AirPods to power next to iPhone.
2. Open Airpods case so it shows connected to iPhone.
3. On iPhone go to Settings --> General --> About and then open the AirPods there.
Then don't touch anything for 15 mins. Usually does it. Sometimes repeating steps 1-3 are required.
My AirPods 3 updated almost instantly.
My AirPods Max sat there ... for a long time... finally I put them back in their case, took them out, plugged them in and ... poof they updated.
I'm no audiophile but I can't tell the diff on the ANC - works just like it did before.
Other topic:
Am I the only one who doesn't like Spatialize Stereo on my Maxes? But on the Airpods 3/Pro 2 I prefer that on.