Barrier

It is a good option alternative to Synergy. Official repo webpage

Download Windows version and Ubuntu version for 20.04

Install on Windows

Install is super-easy as usual. To start up automatically, you might need:

Windows Key+R
shell:startup
Add .bat file, which includes "cd \Program Files\Barrier\ && barrierc -f --no-tray --debug INFO --name minho_linux [192.168.0.10]:24800"

Install on Ubuntu

For Ubuntu 20.04,

sudo apt install barrier

For Ubuntu 18.04,

sudo apt install snapd
sudo snap install barrier

or

Extract the downloaded tar.xz file and move it to the home folder

mv ~/Downloads/barrier-2.3.2 ~ && cd ~/barrier-2.3.2 
./clean_build.sh
cd build && sudo make install  # They installs to /usr/local/

To start automatically when booting, Add barrier shell to the "Startup Applications Preferences". The binary file is in the "/home/minho/barrier-2.3.2/build/bin/barrier"

For start-up as a client, you might need to use the following command: (You might not need it in case you set configuration properly.)

barrierc -f --no-tray --debug INFO --name minho_linux [192.168.0.5]:24800