I would like to report a bug for KUbuntu as there is no working onscreen Keyboard packaged for 22.04. Maliit seems to be a good candidate. Where would it be appropriate to submit such a bug?

If you look at Bug #1947452 you will see that maliit-framework has been removed from Ubuntu jammy on purpose and will most probably not be available in any future (k)ubuntu release.

Reason: Ubuntu-specific, unmaintained, part of a discontinued product;

First of all, thank you for this insight.

While I understand that dropping a package that was not maintained is a logical move, this does not change the fact that ***there is no working virtual keyboard available on Kubuntu 22.04*** (QtKeyboard was also dropped) in particular when one uses wayland (though even on x11 the tablet experience of Kubuntu is not exactly optimal).

Even though I personally think maliit would be the best solution (and is by far not discontinued), I am not a developer . I think the fact that Kubuntu has no virtual keyboard in a time where convertible devices are quite popular is a valid bug (in particular as it used to have one), which I still do not know how to report.

... no working virtual keyboard available on Kubuntu 22.04
Have you tried onboard (no idea whether it works well with Kubuntu)?

... is a valid bug, which I still do not know how to report.
I assume that a bug report to request inclusion of an on-screen keyboard into Kubuntu best fits into kubuntu-meta, https://bugs.launchpad.net/ubuntu/+source/kubuntu-meta/+filebug