If you want banking apps to work, you're fucked. Even getting some of the mainstream social network and chat apps to work without google play services is a pain.
GrapheneOS seems to do pretty well with this. It is a bit more involved and you have to check the docs but you can generally get banking apps to work just fine.
Maybe we need some more economic conflicts, for huawei and xiaomi to switch to their own "play services", and the developers will have to code apps that work on all android variants, not just google-based ones.
There's not a single phone on earth running AOSP, you can't really compare it to Ubuntu. It's not made for tinkering or user ownership.
Sure there are: https://developer.android.com/topic/generic-system-image/
The only project I know about doing that is Replicant and targets ancient phones. It's also a community run project, none of those phone came fully open from the factory either.