The system settings no longer has any way to navigate between primary components. While this could be a nice cleanup of the interface, it is makes it extremely bothersome to navigate without atleast introducing a back button. Otherwise any search for an option involves opening a module, closing the entire app and then relaunching it from the menu (plus a lot cursing, due to how stupid that is).
For the record I am using neon stable. Could it be between versions, and ended up with a broken navigation model?
In neon devedition gitunstable and master build from sources systemsettings5 has the view styles Classic Tree View, Icon View and Sidebar View and in all view an appropriate but different main navigation here. Could you be more specific what is missing for you in which mode, e.g. via providing screenshots?
If you can provide the information requested in comment #2, please add it.
I compared with another computer. It is basically just the toolbar that is gone.
Created attachment 106759 [details] systemsettings
I experienced the same when I updated to master with Sidebar mode and then switched branches to 5.10 which didn't have it. It seems the fallback does not properly re-enable the toolbar. However, now trying to replicate it I always end up in classic view with no issue.
One easy way of making it at least possible to fix when it goes wrong, is to stop blocking the context menu, and allow things like changing the view mode or show toolbar (and maybe even menubar) from the context menu. Could of course also have back there.
Hasn't happened in several months now.