Deactivating multi/split screen?

The third party app is no longer available, does anyone have any suggestions on how to disable this incredibly annoying function?

Multi Window under Advanced doesn't offer the option, only "Split Screen View Action" and "Pop-up View action" both of which are off for me but the split screen still happens all the time when I never want it.
 
The third party app is no longer available, does anyone have any suggestions on how to disable this incredibly annoying function?

Multi Window under Advanced doesn't offer the option, only "Split Screen View Action" and "Pop-up View action" both of which are off for me but the split screen still happens all the time when I never want it.

As of today, in Android 9, there is a blue line between the split screens. In the center there is a short white bar. Swipe the white bar up or down to maximize the desired screen. Split screen is turned off. It is a bit hard to see the short white bar.