How to Start Screensaver with a Keyboard Shortcut on Mac

Part 1 of 2:

Open Automator. If you press F4, it should be in the folder titled Other.
Choose a type for the document. Choose Quick Action.
Search for Start Screen Saver in the top left corner. Double click on it.
Make sure it is set to Workflow receives no input in any application on the right hand side.
Test by clicking on Run in the top right corner. If the screen saver starts, you can press the X button and click on Save, naming it something easy to find (like 'Start Screen Saver').
1. If it doesn't work, read each instruction carefully and try again, or activate screensaver in your System Preferences.

Part 2 of 2:

Open System Preferences > Keyboard > Shortcuts.
Click on Services on the left side.
Scroll down to the very bottom and you will find the action that you created.
Click on the None to the right of the title.
Click on Add Shortcut and type the shortcut that you want. For example, you could use Ctrl+⌥ Opt+S.
Release the keys. The screensaver should start when you press the shortcut.