There’s Mushroom Observer, some people just post there and not iNat, though I feel like iNat still probably gets more usage. Also honestly, a lot of people just post what they find in facebook groups and don’t post it to iNat. The amount of people who are into mushrooms for scientific reasons is a LOT less than people who are just into foraging or psychadelics.
https://forum.inaturalist.org/t/laymans-guide-to-fungus-orders-families/46181/70 I have a bit of a write up on a lot of groups of fungi a few posts down in this thread, though I’m quite busy this summer and I’ve got a website I’m slowly chipping away at now so I doubt I’ll be updating it anymore. Also for the US, especially the midwest and east, I can’t recommend mushroomexpert.com enough. For the pacific northwest, Danny Miller has a website cataloging all of the sequencing finds out there (https://www.alpental.com/psms/ddd/) but he’s got some good pictures and I definitely reference his site a lot. Also, there’s Amanitaceae.org, which is Rod Tuloss’s catalogue site for amanita. Finally, there’s the Bolete Filter (https://boletes.wpamushroomclub.org/) which isn’t perfect but it’s pretty good at at least ballparking stuff - I find it to be fairly good for my area but I’ve heard its less accurate in regions that aren’t in the same ecoregion as Pennsylvania.
EDIT: Field guides are weirdly, kind of less useful, because a lot of them are really behind on science and tend to use European names for some American fungi. They’ll get you to genus but the species usually isn’t accurate. Not that they’re all bad, there are some very good ones, and are still worth picking up
EDIT 2: for what its worth, you don’t have to get good at IDing ALL species of fungi. Just pick like… one or a couple, learn what it looks like, and learn what the lookalikes like. Once you’re comfortable with that, learn a different one. For example, one easy way to help would be to read through this paper https://fuse-journal.org/images/Issues/Vol14Art9.pdf and then go start working on iding Macrolepiota observations in the US, avoiding the west coast and the southwest since we have sequences of not-yet-described species from those areas. I went through when this paper came out and knocked all of the incorrect Macrolepiota procera IDs to the proper species but there’s a lot of observations at genus level that are going to take a long time to work through. They’re pretty distinct mushrooms and the biggest two look alikes you’re going to see mis-ided as macrolepiota are Chlorophyllum molybdites and Chlorophyllum olivieri, but they both lack the chevron/snakeskin patterning on the stem.