I bought two AirPod Pro sets for my partner and I, and both have the same problem (firmware 3A283). In noisy or windy environments, the speaker's voice is intermittently severely muffled. The muffling seems very similar to @mdadk 's test on page 7 with recordings from an airplane: https://www.dropbox.com/sh/uhbhtxu7le71can/AAB-F6NkTy4Pcf97RX15lT1ja?dl=0
During my own testing, I found that background music volume was reduced even with a single AirPod microphone, implying that an algorithm always attempts to identify background noise (i.e. not only filtering via multiple microphones)
From my experience, it seems that the muffled voice problem appears around sharp noises, traffic and even slight wind, apparently by reducing the speaker's voice along with the background noise. It is annoying that there is no way to turn off this behavior, since the phone microphone appears to deal with it fine, by allowing more background noise. This is very clear in the airplane recordings mentioned earlier.
It might be possible to reproduce the issue by playing a recording of street, kitchen or white noise while talking.
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Unrelated to this issue (?), there seems to be a different microphone-related problem in the recording provided by @hakakaha on page 20, who recorded at home with some music in the background: https://1drv.ms/u/s!AjkBPOBNj27Cg69GX5fi9Px17Ra6Cg?e=5jFdTf
I tested the latter while using either one or both Airpods as the microphone, and could not reproduce this behavior.