Dang, I've been using sync for more than a decade, and even I did not know that sync had multi window support on Android. I think there needs to be a continuous education workshop, video tutorial series, or a sphinx style docs site on all these features when the beta dust settles. Multi tasking is so handy. FYI:
This screenshot was from a Samsung Tab S8 Ultra. You can run 4 onscreen apps at a time (if you include a floating popup window in the mix) with multi windowing on Android 13 (outside Dex).
Getting the screenshot took a little tinkering, as after the first window split, getting the third instance of sync on the screen required using the Samsung side panel to drop an unrelated app in the third quadrant, then using the launcher to alt-tab the display to Fullscreen the third instance of sync, then alt-tabing back to Fullscreen the 3 app multi window view, then using the quick app switch gesture to swap out the unrelated app for the third instance of sync. It was a little overly complicated.
Multi tasking and window tiling in Samsung Dex is a lot easier, or more intuitive, to replicate the kind of thing, but I still prefer androids native launcher layout, as app windows don't have needless title bars, and the same navigation gestures work better when not breaking out the mouse and keyboard.