I thought AirPods Pro 2/3 already had custom EQ, because EQ is one aspect of configuring hearing aids to a particular person's hearing deficits.
I searched for these keywords:
configure airpods pro for hearing deficit
A top result from Apple Support:
AirPods Pro 2 and AirPods Pro 3 provide a clinical-grade Hearing Aid feature for perceived mild to moderate hearing loss, as well as a Media Assist feature that enhances the clarity of music, video, and calls.
support.apple.com
On that page, the link under "Audiogram results ..." leads here:
Your AirPods Pro 2 and AirPods Pro 3 support your hearing health with Hearing Protection, on by default, and a Hearing Aid feature.
support.apple.com
Item 6 under the heading "Add audiogram results from your hearing healthcare professional" ends with "or enter the results manually."
To me, this looks like it should be possible to enter some kind of parametric gain/attenuation values in dB, at certain frequencies, producing a custom EQ curve. That's probably not something one does casually, or even interactively, but it seems possible.
Since I don't have AirPods Pro 2/3, I can't see what any of this looks like, nor the range of values supported, nor what interface is presented to "enter the results manually".
One interesting possibility might be to have an app you tweak interactively, and it then displays an audiogram as if it were done by an audiologist, then use the "Scan audiogram with camera" feature also listed in item 6.
Anyway, one other thing I'm curious about is if the new custom EQ feature would be combined with the audiogram parameters to make a new overall EQ curve, or whether the EQs would remain separate.