You can disable Synergy temporarily by stopping the background service. We'll be adding a feature to do this in 2.1 which is due early 2018. Until then, it has to be done manually.
Windows:
Open the Services program (Run > services.msc) and find the Synergy service. Double click it to edit the service, and choose Manual from "Startup type", then click Stop to stop the background process, and Start to start it again.
macOS:
Open the Terminal app and run this command:
launchctl unload /Library/LaunchAgents/com.symless.synergy.synergy-service.plist
To enable it ag