Using multiple screens, how to switch spaces on all screens left or right
Only by not using  System Prefs > Mission Control > Displays have separate Spaces.

Once you do that, all 3 screens will 'share' the same space &amp; switch together.



Personally, I find it a much better way to work, but I guess it will depend on personal preference. Using this method I like to 'tie' certain sets of applications together so I can see each 'set' on a different Space.

Each time you swap methods, all your carefully-prepared Spaces will mess up, as the numbering will change, so be prepared to have to reset which apps are set to open on which Space, if you wish to try it out.