PINE64

It was a deliberate decision by the KDE developers to not port their existing desktop applications to mobile platforms, but instead develop new mobile or convergent (i.e., both mobile and desktop) applications from scratch using QML and Kirigami instead of QtWidgets. Neither the Qt project nor the KDE project is interested in QtWidgets for touch environments, so its support for those is very poor.

Before the developer quit, Plasma Mobile Manjaro build was really good on a tablet, including on screen keyboard. Daily drivable in my opinion. The latest build has completely fallen apart. But, try a March or April build. You can build plasma mobile for postmarket (x86 or arm) but it will not be as complete as the Manjaro build was.