libgtkmm-3.0-dev 3.24.2-1 (i386 binary) in ubuntu focal

 Gtkmm is a C++ interface for the popular GUI library GTK+, API version 3.0.
 Gtkmm provides a convenient interface for C++ programmers to create
 graphical user interfaces with GTK+'s flexible OO framework. Highlights
 include type safe callbacks, widgets extensible using inheritance and
 over 180 classes that can be freely combined to quickly create complex
 user interfaces.
 .
 This package contains development files and examples, as well as a
 gtkmm-demo program.