I like GrapheneOS. Not sure if this fits your use case or not. It is an Android-based OS with a focus on security. By default it has no real app store, and no push service. It's basically a hardened AOSP with a bunch of security focused modifications. It runs on Google Pixels only, because (they say) Pixels are the only Android phones that meet the security standards of the project. But don't be fooled, GrapheneOS is completely degoogled. No account will be needed or prompted for.
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I like GrapheneOS. Not sure if this fits your use case or not. It is an Android-based OS with a focus on security. By default it has no real app store, and no push service. It's basically a hardened AOSP with a bunch of security focused modifications. It runs on Google Pixels only, because (they say) Pixels are the only Android phones that meet the security standards of the project. But don't be fooled, GrapheneOS is completely degoogled. No account will be needed or prompted for.