One of the nicest upgrades in OS15 was the ease of adding an app not in the dock to split-screen. How do I add an app from the Home Screen or App Library to one of the Stage Manager groups?
Well, for me… my setup has always been to keep all my apps on the dock. This helps me to quickly multitask through the dock… drag & drop along with having the App Library always accessible.
Another tip. You can use Spotlight to quickly access an app.