Section groups in OneNote for Android are not foldable.
Part of my Note Collection is higly organised based on section groups.
Browsing those notes on the Android app is not convenient
It's the only OneNote client that i'm aware off that lacks this (basic) feauture
(The IOS App has it, as well as OneNote and OneNote for Windows 10, Webclient , ...)
In my case, it greatly reduces the usefullness of OneNote .