SUMMARY
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My setup (handheld device with touchscreen) was fully set up and working with Plasma 5, but after updating to Plasma 6, the Maliit keyboard no longer shows up anywhere.
***

Hello there, 
and sorry for filing this as generic - I am not sure which specific component to file it under.
However, as the issue started with the update to Plasma 6, I am reasonably confident that Maliit-keyboard is not to blame for this.

I am using a handheld based on Intel's i7-1165g7 with a touchscreen.
As the device does not come with a keyboard, I am relying on Maliit for all touch typing, including unlocking the device from lockscreen.
With the device being portable and a single user device, I am automatically logging into my user via and then locking the session via a simple autostart script. (SDDM is uninstalled, not used)
This way, the device boots fully into Plasma and then drops me on the locked screen, which I used to unlock via the touchscreen.
However, the update to Plasma 6 broke this workflow, as I can no longer get maliit-keyboard to open.
It used to open by simply touching the line where I enter the password (nope), or when touching the virtual keyboard button on the bottom left of the screen (nope), or when touching a terminal window (nope), or when touching the Firefox URL bar (nope).

My ~/.config/kwinrc still ends with these lines (did work previously):
[Wayland]
InputMethod[$e]=/usr/share/applications/com.github.maliit.keyboard.desktop
VirtualKeyboardEnabled=true

[Xwayland]
Scale=1

And "Maliit" is still selected as the Virtual Keyboard under System Settings.

I have also tried reinstalling maliit-keyboard, as well as plasma-desktop (yay -S --asdeps $(yay -Si plasma-desktop | grep Depends | cut -d':' -f2)  ) but no luck with either.

STEPS TO REPRODUCE
1. Install the latest version of Plasma 5, install and set up maliit-keyboard
2. Update to Plasma 6

OBSERVED RESULT
3. maliit-keyboard no longer opens

EXPECTED RESULT
3. maliit-keyboard shows up and allows touch-typing

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux (6.8.1-4-cachyos-lto)
KDE Plasma Version: 6.0.2
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2