The (shift+)cmd+` order also resets to match the window z-order whenever you switch apps. So if the order is windows A, B, C, then you select window B, cmd+tab away, then cmd+tab back, the order will now be B, A, C.

I've developed an intuitive understanding of this, but I had to experiment just now to describe the behavior precisely. And my intuition is still wrong sometimes (like if the app has windows on multiple monitors, it's hard to predict the z-order).

> if I Slack open in Firefox in workspace 1 and Outlook open in Firefox in workspace 2, there is no way to switch between Slack and Outlook

My local maximum is to never use workspaces – just cmd+tab, cmd+`, and sometimes cmd+h to reduce screen clutter.