No doubt that Synergy is a great tool. But shifted into closed source and lack of update for open source version makes it difficult to work across all platforms. Synergy is available on pacman. All you need to do is sudo pacman -S synergy. It's that simple but on Ubuntu 20.04 or similar Ubuntu based debian distro there is no easy solution. Most of the .deb are old. After searching for a while find a blog post from Florian Panzer where he rolled his own .deb package.

Blog Post: https://rephlex.de/blog/2020/04/24/synergy-1-11-1-package-for-ubunu-20-04-focal-fossa/

Mirror Download Link: https://github.com/shawonsaha/shawonsaha.github.io/tree/main/files/synergy_1.11.1_deb