RustDesk is a fully free and open source remote desktop software. It's an alternative to TeamViewer, AnyDesk, DWService, and it is the only one to be fully open source, because both client and server are under GPL.
Unfortunately they don't provide with any flatpak, snap or appimage at the moment.
(since solus goal is not to be used as a server I'm only requesting for the client here)
https://github.com/rustdesk/rustdesk
Latest sources : https://github.com/rustdesk/rustdesk/archive/refs/tags/1.1.9.tar.gz