I know this is a big request but this will be amazing. There are not many apps that allow you to send/receive SMS messages from the desktop that sync to your phone, especially ones that use encryption. If a desktop app can be created for Windows, Mac and Linux which will be able to pair to multiple phones and allow you to send and receive SMS messages on your desktop.

The syncing will have to be done using encrypted even for SMS messages that are not sent using encryption but the Signal protocol should work fine for this. And the syncing should not be centralised (No servers needed) using Peer-To-Peer connection between your phone and the desktop device.

It will also be amazing if the desktop app is able to answer and receive phone calls on the desktop, but I already know I am asking for a lot with just a desktop app alone.

There is no way to send or receive SMS messages on your desktop using a Android phone that is deGoogle. There are apps that allow this in the Google Play Store but not on F-Droid. I do think Silence will be the perfect app to do this since the SMS app the the only SMS app I know that can encrypt text messages.