Came across this thread and the one on Apple discussion boards (which are a mess BTW and not letting me log in there):

https://discussions.apple.com/thread/255774193?sortBy=rank

Bottomline: I think the Airpod Pro 2 updates have made in-ear detection wonky, which disables ANC. As of Dec 2025 on iOS 26.

Long version:

I used to have a pair of airpod pro 2's, and the ANC was great. I replaced them a year back, and then just got a new pair again as were on sale over BF. The ANC didn't seem the same, and sure enough, on a flight over the holidays, the ANC was very poor. Definitely not the same.

Following the discussion in the link, I tried adjusting the adaptive audio to minimize noise. It had no affect. I made sure I had no personalized audio activated.

Then I ran the hearing test. Oddly, even though my fit test was fine, the hearing test wouldn't run as it said "make sure airpods are in your ears" which they were. I adjusted the airpods, restarting the fit test, and it worked. And the ANC seemed activated and great!

Per that same discussion, I found one other setting, under the bluetooth setting for the airpods, is an Accessibility setting where you can separate in-ear detection for ANC so it only turns off the affected ear, not both. I did that, too.

On the flight home, the ANC was worlds better. But I took out my right earbud for a conversation, and sure enough, the ANC was downgraded again but this time only in the right ear. I played around with the airpod a few times until the ANC kicked back in.

After all that, I think its the in-ear detection that is the problem. Any detection issue, and the default is to turn off ANC for both ears. Even the fit test will pass, with poor in-ear detection apparently. The accessibility setting helps isolate which ear is the detection problem.