Split View and Slide Over was useful. It used to be really easy to add an additional window/app next to the currently open app. But now it requires fiddling around with resizing windows and arranging them in the right way. Many more steps. I can now open more than 2 apps simultaneously, but more than 2 apps just don't fit the screen of an iPad.

PS: they brought back the option to just drag an app from the dock to enable Split View, but it's still not as smooth as it used to be before 26.

Same here. I much liked split view and slide over. The current features made it such a hassle that I just switched back to single full screen apps.