As someone who is beginning to really dislike both Google and Apple, is it possible to buy/use an Android phone without the Google store where you only sideload software?
Totally ungoogled you won't have the google service layer, if you still want to use some proprietary apps, it is possible but some won't work. The biggest constraint is often push notifications not working.
As an alternative you can use microg [1] which is a client side re-implementation of google services. Some part uses alternative service as backend, some will use google though, like push notifications.
Side loading can have its limitations has you need to find sources for APK that you can trust.
The best non google store is f-droid [2] in my opinion, all open source and build reproducible.
If you need some proprietary apps from google store, you can use the client Aurora Store [3] which still sources app from google play store.
In term of buying a phone with most of that, /e/ does sell phones with android + microg + their own store [4]
Otherwise plenty of phones allow to easily replace the operating system. You can look for phones supported by lineageos which comes with no google apps. [5]
[1] https://github.com/microg [2] https://f-droid.org/ [3] https://gitlab.com/AuroraOSS/AuroraStore [4] https://e.foundation/ [5] https://lineageos.org/
It's not as good as micro g or a completely ungoogled phone but the benefit is you can use manufacturer roms with all security features like bootloader locking turned on.
I do this with my OnePlus as I don't like leaving the bootloader unlocked. Anyone can pull a disk image off it through recovery then.
Another benefit of this is that Google play services like location and push still work, they don't require an account. But you do give up extra privacy compared to the other options.
There are grapheneos and calyx which do allow bootloader locking but they only work on pixel phones and those are really poor value for money IMO (expensive but still having fingerprint on the back, midrange soc etc). And really hard to get in Europe now. The 5a 5G is not coming here and probably the 6 isn't either.
So this is why I ended up with this option. At least Android has a wide spectrum of choices. With Apple it's take it or leave it.
Apps that support it: https://unifiedpush.org/users/apps/
They're coming back from that now because nobody wanted it but I don't doubt they still want to create their own walled garden. It's free money off app sales, control that gives them leverage over their customers and develops, data which they love (they're always pushing telemetry).
I don't really see what's in it for them to make a really open store.
Look at Amazon App Store, and it's failed Fire Phone. Amazon has cornered the market on low-end tablets with it and people still try and install Google Play Store on it. And according to Epic's lawsuit, Google has been actively preventing hardware manufacturers from packaging alternative app stores with products.
Also the Huawei AppGallery outside of China since they lost access to Google apps.
Here's one page about it, I'm sure there are plenty more.