Source (link to git-repo or to original if based on someone elses unmodified work): https://github.com/MakG10/plasma-applet-display-profile-switcher
Applet for KDE Plasma 5 to switch between display configurations. For example, you can easily switch between single and dual monitor setups or cast screen to TV on demand.
How to use?
1. Open plasmoid’s configuration.
2. Click “Create profile from current setup”, edit its name
3. Go to KDE’s display configuration in system settings and change monitor setup
4. Return to the plasmoid’s configuration and add another profile
5. Now you can switch between profiles by clicking on their names