I’m getting this same issue, also with Android (v.13) and app version 1.29.14. The last time I uploaded a sighting was September 19th and I don’t recall having this issue; my phone hasn’t updated since then so it must have been an app update that broke it. Gallery is working with photo picker integration in other apps, it just seems to be iNat that it’s broken for.
I have no idea why “bug reports” is apparently an option, but gallery and photos aren’t (although it is somewhat ironic).
Anyway until the issue is fixed I’m afraid I’m unable to use iNat at all as all my photos are stored and organized on my phone and the web version is a nightmare to navigate on mobile. :(