You can sell the phones alright, and they might even work, but the fact is that participation in society - especially if you live in a city - will be much harder without Android/iOS.

Note, not impossible: You can always carry cash to avoid phone-based bank payments (which would be needed at e.g. my local farmer's market, where nobody has a card payment terminal), some taxi services (Yandex Go for example) provide a web view with some of the features, you can open map services in the browser ...

But for the browser-based cases the experience will be even worse than the standard app experience, and friction is overall much higher.

As a result, only a very small fraction of nerds are committed enough to buy and use these devices. You then have a chicken&egg problem about getting a third option to work.

The only way this has been done semi-successfully in recent years is Huawei's HarmonyOS - and they did it by way of a) already being an absolutely massive phone company, and b) keeping around an expensive Android-compatibility core for many years.

Yes, the chicken and the egg problem. But here is the thing, the more adopters there are the more likely to get support. Not to mention the userbase will be mainly in the EU.