Using gtk without installation

hi, I am trying to use gtkmm4 without installing it. I added the location of the headers and libs to my project (cmake) and I copied the icons to my app folder. First run was ok, than I added a combobox, and got a warning: “pan-down-symbolic.symbolic.png: Image type “png” is not supported”
followed by an error: “Bail out! Gtk:ERROR:./gtk/gtk/gtkicontheme.c:3823:icon_ensure_texture__locked: assertion failed: (source_pixbuf != NULL) Aborted (core dumped)”.
I installed libpng and rebuilt gdk-bixbuf, and I still get this error.
Debugging the app showed the icon was expected to be found in: /org/gtk/libgtk/icons/16x16/actions/
I looked up gtk icons issues, and found it may be related to caching the icons folder, which I’m not sure where is the LoaderDir in case gtk was not installed. I tried to specify another loader dir using GDK_PIXBUF_MODULEDIR, but results are the same. Could you please help?