Disabling folder view is by design temporarily because KDE devs are revamping code. It should be back by 5.12. If this dev post is any hint, it means that distro maintainers are able to enable the folder view widget if they want to
https://blogs.kde.org/2018/01/24/and-again-story-kde-plasmas-desktop-icons-512-improvements
Someone pointed ot where folderview widget settings are saved on Plasma 5. Maybe that could help?