This is a usability problem in v5.1: many users have been fooled by the top level tree items which can instinctively be taken as empty, but they are actually pages. In 5.99 this has been fixed and clicking a top level items leads to its first child page.
You have to tolerate that still for v6 when it’s released. But then the major changes to the preferences structures have probably been made and moving to v7 will be easier in that respect.
This seems to be an eternal question in user interface design. Either you keep the old bad UI and make transition easy and old users happy, or you make the interface better and intuitive for new users but drive old users mad. The KiCad developers take usability seriously and have chosen to make the interface better.
Being a relatively new user to Kicad (September last year) finding settings in the menus was one of the most challenging parts of of the transition. Once I had decided I was going to start using Kicad full time I spent a while going through all the menus and trying to work out what each setting did. This helped a lot in the use of Kicad and saved many hours of troubleshooting as I already had an idea of where the settings were.
I picked Kicad up very quickly (despite the interface) but this could be down to the 20+ years of pcb design experience, I imagine to a hobbyist starting out it would be daunting.