- Find an open-source software that you’re interested in, but your main distro doesn’t provide it in the official repo. Be a packager for this software.
- Open your distro’s wiki, rewrite (or contribute, if already good enough) a page or section.
- Try the bleeding-edge version (or very-early testing) of your favourite distro, and submit some test results, regarding to your hardware.
IMHO these tasks are interesting, could learn a lot from these tasks, and other linux users could benefit from these work
KDE Connect: https://kdeconnect.kde.org/
I also use Resilio Sync. It’s not open source software, but it’s self-hosted https://www.resilio.com/
There are also open source sync services, like nextcloud or syncthing