Looking for recommendations for an open-source, peer-to-peer clipboard sync that works across iOS, Android, and Windows and Linux, with no central servers or accounts, best to have end-to-end encryption). Does anything like this already exist, or is this still an unsolved gap?
Blip is a good option. Not on Linux yet but they are making an app.
If everyone submits feedback on how they want the app it will turn out how we want it. So some basics being Flatpak & AppImage support