As a workaround you can use https://github.com/Supreeeme/extest to make Onboard work. Compile it as a 64 bit library and launch onboard with
env LD_PRELOAD=/usr/lib64/libextest.so onboard
If you want to use it with KDE you can add
X-KDE-Wayland-VirtualKeyboard=true
to its desktop-file.
I used k...
Finally the Onboard on screen keyboard works on Wayland
This is too great not to share. Wayland devs hate this trick! I'll copy what I did from the bug report.
As a workaround you can use https://github.com/Supreeeme/extest to make Onboard work. Compile it as a 64 bit library and launch onboard with
env LD_PRELOAD=/usr/lib64/libextest.so onboard
If you want to use it with KDE you can add
X-KDE-Wayland-VirtualKeyboard=true
to its desktop-file.
I used kwin rules to get rid of window decorations and have it always on top without stealing focus. If someone knows how to make all other windows smaller when it's active that would be great.
Only problem remaining is that sometimes the keys get stuck on touch input. At least on my Steam Deck on OpenSUSE.