Not OP but my layman's understanding is that it would just be two GUI windows communicating over standard IPC. The current trend is for the entire application to be represented as a singular window, using navigation or tab controllers to switch between views rather than popping them out into their own windows.
Better window management paradigms aren't quite what I was referring to, but would also be great for mainstream software vendors to not have given up on. I use the Sway compositor on my personal machines to get some sort of reasonable window management tooling, which is lovely to the limited extent that even Linux software embraces composability in graphical environments. Would be nice to have similar tools on my work macbook.
With my particular workflow, tiling functionality without window-manager-level tabs is not enough of an improvement over the window snapping I can get with BetterTouchTool to justify another tool, but I am quite pleased with the availability of good third party window management tools on macOS. I understand that many people find tiling on its own quite useful (and my reliance on tabs restricts me quite a bit on Linux as well — to Sway, i3 and the ancient Notion).
Windows has at least one tool for tabbed windows though! Check out Stardock Groupy if that sounds like your sort of thing (and I swear there was another one but I can't find it, maybe Groupy is a rebrand?)
More precise would be to say "graphical IPC control" or "graphical IPC initiation." I'm trying to point to the ability for users in a graphical environment to coordinate intricate communication between processes. Copy/paste and drag-n-drop are canonical examples, but I'd say that macOS tools like Alfred should also count.