Regarding gtk-update-icon-cache, this is not supported in the minimum meson version. Recently such funtionality (to run scripts after installation within the install directory) was added to the gnome module, see https://github.com/mesonbuild/meson/issues/8268
Does anyone know the impact of running this program (or more specifically, of not running it). My understanding is that packagers don't need it (because they usually set DESTDIR to install the binaries to a staging directory, from where the actual package is created) and run gtk-update-icon-cache as part of the package installation. But what's the impact for custom installation, e.g with prefix = /usr/local or something under $HOME ?