Go for a prepaid provider and give out as little personal information as necessary. Avoid the major carriers directly because they need a social security number.

That said, mobile phones are inherently not private. No matter what provider you choose, they will be able to track your location using tower triangulation. Even if you give a fake address, it would be pretty easy to identify you if you always have your phone on at home.

This is very disappointing.

What we would need on the long run is simply replace email with a common standard

That would be ideal, but realistically, if email ever goes away, it would be replaced with a proprietary locked down ecosystem. Likely a messenger app. Link a WhatsApp or Facebook account and you will get messages and notifications through that. I just do not see current tech companies supporting a new open standard for communication.

Despite all of emails flaws, it is one of the few remaining universal forms interoperable communication with little vendor lock-in. It would be great to have something more modern, but not at the expense of openness and interoperability which is likely what would replace it at the current time.

A GitHub issue was opened for Syncthing-Fork, so it will be worth watching that to know whether it will continue to be supported.

This does not apply to the server. Only the client app is open source. The server is proprietary.

Proton will still be a for-profit company that will be majority-controlled by a non-profit. The non-profit will not own all of the business either, so there will still be profits going to shareholders.

Which is the same structure that Proton is moving to.

Plus donations to Mozilla cannot even be used for Firefox development due to the structure of the foundation and corporation.

Graphene OS > iOS > Stock Android

The same is true for stock Android devices. Unless you are using a custom ROM without Google Play Services, there is more proprietary software than open source running on Android devices.