Add Dock Spacer on Mac

1. Start Terminal.

2. Run command to create spacer:
   defaults write com.apple.dock persistent-apps -array-add '{"tile-type"="spacer-tile";}'

3. Reload Dock:
   killall Dock

4. Run the following commands below.

5. Close, re-open and re-run commands in step 1 in Terminal to add extra spacers.