About two years ago, I posted mushrooms twice on iNaturalist (not Seek) and quickly got updates with a more specific identity from other users, so I think there is an active community out there. They were amanita muscaria -> american amanita muscaria and oyster mushroom -> summer oyster mushroom.
The only non-mushroom confirmation / corrections I've gotten on iNaturalist were a spider and a snail.
That said, it may be tricky to get a good identity on mushrooms. There are some varieties need spore prints or very careful attention to structure to identify.