This was one of my early – and consistent observations about stage manager – it works fantastic in a single-display environment. But from a workflow standpoint, it does not work as efficiently across multiple displays. I’ve written about this before here, along with a collection of my other thoughts on Stage Manager:
It might work better for multiple monitors if the two displays were treated as a single, unified stage. As it is, it’s inefficient to move windows from one display over to the other display and onto the right stage on that other display.
If Apple brought some of the Stage Manager controls from iPad over to the Mac, it would probably also solve a number of this problems. E.g., using Globe+^+\ to move a window from ipad to display and vice versa would be very useful on mac Stage Manager.