Is this what you're doing?
Tap on a shape (the Touch Slide open with it).
Tap either of the finger guides (the concentric circles) to get the shape you want to modify (only circles, squares, and triangles).
Once you see the shape you want, it can be enlarged/reduced by placing fingers on either edge of the outline and dragging/pinching.
When you have the size you want, long-press on the outline. Depending on where on the outline you long-press you'll either see a vertical line or a horizontal line in the middle of the shape. As soon as you see that... Drag.
Give that a try and let me know how it goes.
Still doesn't work for me. Every time long touch on the outline I get the Fill icon with an x over it. I can never trigger the line down the middle no matter how many times I long press the outline of the rectangle.
If you're getting the Fill icon, it seems like maybe you're missing the line. A couple things: Your finger guides are still on the screen when you're long-pressing, right? Maybe try a lighter touch on the line. Aim toward the outside edge of it. Maybe ever ask someone else to give it a try.
I thought for a moment that maybe it didn't work on iPad Pro but I asked someone to test it for me and the feature seems to be working fine.
I'm sorry this is such a hassle.
I'm having the exact same problem on the iPad Pro, I just keep getting the fill icon with the x.
My apologies, I just this minute realized something... the iPad Pro version of Adobe Draw is not out yet and the person who tested probably inadvertently tested on a beta version of the app. The iPad Pro version of Draw will be available VERY soon, so hang in there with a few of the previous features that might not be working yet.
OkieKidd, sorry for all the back-and-forth and wasted time not being able to get the feature to work.