The Qt Virtual Keyboard [1] isn't exposed anywhere except the login screen. There are no options anywhere to find it in the accessibility settings. I have not confirmed if this is different in the wayland session [2]. For users who cannot use a keyboard (this can be for various reasons such as: no keyboard, defect keyboard, having a mobility impairment) this is a big usability issue. And if you don't have a keyboard you cannot enable per-application virtual keyboard with QT_IM_MODULE as a workaround because that would require text input.

A promising candidate is qvkbd which is already in some distro repos [3]. It has an indicator that integrates nicely with Plasma for easy hide/show. It's missing some nice-to-have features but it is a huge improvement over the current situation where users on X11.

[1] https://packages.ubuntu.com/source/bionic/qtvirtualkeyboard-opensource-src
[2] https://blog.martin-graesslin.com/blog/2016/05/virtual-keyboard-support-in-kwinwayland-5-7/#comment-70808
[3] https://build.opensuse.org/package/view_file/X11:LXQt:git/qvkbd/qvkbd.spec?expand=1 https://aur.archlinux.org/packages/qvkbd-git/