There’s no proprietary apps on F-Droid. It doesn’t even have Signal which is open source.
I’m not sure what’s your pain point then? With Aurora you can install and automatically update proprietary apps. You can use anonymous accounts so you are not officially logged in (does this still work?). If you want FOSS, then fdroid. There’s more updating tools such as unobtanium, but seems what you want is Aurora.
I’d just like to be completely free of Google’s app distribution infrastructure if possible. I’ll have to look into unobtanium. I haven’t heard of that one previously.
Google s is the largest, but not the only one. Amazon, Samsung and some OEMs have their own app stores too.
There are alson sites that archive and distribute apks, like Apkmirror.
I have a tablet logged to nothing (as in no account, not the OEM) and all my apps come from fdroid, obtanium or apkmirror.
It started as an experiment, and honestly it’s (for me) not a big hurdle, but an app store would make things easier, that’s for sure.