How to switch from from the active application on monitor 1 to the active application on monitor 2 via keyboard
Based on your original question here is the answer to that.


  switch from one active desktop to next visible desktop on other
  monitor




On High Sierra the keyboard shortcut to switch Desktops already exists.



In my case it only shows 1 since I only have one Desktop.

In your case it should show 8 Desktops (numbers)