Me too! It works in most of my projects, but with my 20-year old macOS project which I converted to a workspace a few years ago, clicking on the project name there never shows that "second sidebar", as you call it. It shows me the raw text of the .pbxproj file instead. I'm not sure, this may be the first time I've tried to edit a Target Setting since updating to Xcode 26 beta. Did you ever figure this out? Thank you.

I solved the problem. I had switched on the "Code Review" button (icon left-pointing arrow above right-point arrow) in the top right area of the middle (code) pane.