It might be just down to your gestures/finger movements.

Try dragging your first app window down from its top title bar (as if to close app) but stop half way down the screen with your finger and drag app to either left or right. It should go to split screen mode - I just tried it and it appears to work in both Tablet Mode on/off.

If you have two apps open in split screen mode, opening a 3rd app will not be docked to either left or right side. You will have to drag the application by the top title bar and manually drag it to the left or right side of the screen. The two docked windows created earlier should remain in their places even with a 3rd and 4th window docked over the top.

I didn't make any specific changes to any setting to experience this so it ought to work on your tablet too

Thanks for the response! I think I'm doing it right, the gesture/finger movement for both table mode and desktop mode is the same (and it works in desktop mode), and I used the same gesture on my 2-in-1 device in tablet mode and it works just fine. When you drag your finger down halfway, the window shrinks, move your finger to the right or left and it moves, but when you get to edge instead of docking it goes full screen.

I spoke with Dell Tech support and they remote desktop'ed into it and tried to see what was going on. They claim that in Tablet Mode windows are set to 'full screen only', they can't explain why it works on my other computer. Or how to turn off or where the setting 'full screen only' in tablet mode is? Is this a preinstalled Dell bloatware setting?

Thanks!

Settings > System > Multi-Tasking

I have all of mine turned on

Settings > System > Tablet mode

I have both turned on

I currently cannot see any other settings that might affect Tablet/Desktop modes but if I do I'll share my findings

Thanks, I'm starting to think this a touchscreen hardware or touchscreen driver problem.

I solved the Multitask problem!!!!!! Well sort-of:

I went side-by-side with my devices and started matching every single setting (not just multitask and tablet mode) from my device that worked to this device and it didn't take long; the top setting System > Display > Change the size of text, apps, and other items by default on this device was set to 200% and on my Lenovo was set to 100% (because it has a 15" screen not an 8" screen), so I changed it to match and right out of the gate it worked! By Trial and Error I got to 175% and it still worked (I can only make the scroll bar go in 25% increments). So by further trial and error I found Control Panel > Appearance and Personalization > Display > Set a Custom Level and set it up to 185% anything above that and it didn't work.

If you or anyone else still need a solution for this issue (most/all applications open maximized regardless of last saved state) let me know.