Dear Maintainer,

* What led up to the situation?

No GTK4 immodule support in uim-1.9.7 even though uim itself supports
it.

* What exactly did you do (or not do) that was effective (or
  ineffective)?

Checked debian/rules.

https://salsa.debian.org/debian/uim/-/blob/master/debian/rules?ref_type=heads#L35-36

It seems that it should add libgtk-4-dev in debian/control and
--with-gtk4 in debian/rules. It also shape uim-gtk4 package like
uim-gtk3.

nitpick: meaningless --with-gtk option is specified.
It should be removed.

Best Regards,