Since Plasma 5.10.95 (Plasma 5.11 beta) the touchpad input clicks or tabs are inaccurate on Wayland e.g. in Firefox, Qupzilla or the Konsole when marking/editing text. I assume this is because on my 4k notebook screen a scaling factor of 2x is applied automatically.
For me this bug has been fixed with Plasma 5.11, maybe with https://bugs.kde.org/show_bug.cgi?id=384769.
Thanks for the update. Glad it is fixed. *** This bug has been marked as a duplicate of bug 384769 ***