There is yet another option that's completely free and requires no third-party app. Be aware that I've only tested this on MacOS latest version Catalina (as of now).

1. Go to System Preferences
2. Select Keyboard and then the Shortcuts tab
3. Then on the list that appears select App Shortcuts
4. Add new shortcuts like this:
   • Click on the plus sign to add a new one, the Menu Title field has to match exactly the text that appears on the Window menu in every application: "Move to DISPLAY NAME" (To find the text just open the Window menu on any application)
   • Finally on the Keyboard Shortcut field enter the shortcut you'd like to use
   • Add as many shortcuts as you need to move any window between your displays!

There is yet another option that's completely free and requires no third-party app. Be aware that I've only tested this on MacOS latest version Catalina (as of now). For other OS versions see Create keyboard shortcuts for apps on Mac

1. Go to System Preferences
2. Select Keyboard and then the Shortcuts tab
3. Then on the list that appears select App Shortcuts
4. Add new shortcuts like this:
   • Click on the plus sign to add a new one, the Menu Title field has to match exactly the text that appears on the Window menu in every application: "Move to DISPLAY NAME" (To find the text just open the Window menu on any application)
   • Finally on the Keyboard Shortcut field enter the shortcut you'd like to use
   • Add as many shortcuts as you need to move any window between your displays!