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Ifixit gives fairphone 5 a 10/10 on repairability and maintanence
(www.ifixit.com)
This is a most excellent place for technology news and articles.
You need a Google account just for the Play Store, given that it's a Google product.
You can download apps from other stores just fine: install F-Droid for example, or Amazon which has their own app repository too, and you'll be able to download and install apps from there. (I don't recommend using Amazon, it's just an example)
For apps on the Play Store, you can use Aurora Store which proxies the Google Store and does not require a Google account.
And you can prove that the binaries I receive are the binaries from the developer?
F-Droid has reproducible builds, so definitely yes. You can even check the exact code used to build every app on F-Droid.
The rest of stores, it depends. Every store has their own policy and the only one I recommend is using F-Droid or downloading directly from the devs' website or Github repo. There's an app to automate this process for updates too, so it's actually a quite good method.