run make gtk3 for testing the gtk3 version,
and make gtk4 for the gtk4 version.
This seems to only crash when the tooltip is actually displayed:
see make query-no-display which is the same as make query4 but
WidgetExt::connect_query_tooltip()'s callback returns false, so it is not displayed.
There is also make set3 and make set4 that use the WidgetExt::set_tooltip_text()
instead of using the builder. The issue is still there.
I'm pretty sure it is just displaying the tooltip that is the issue, I don't know enough about gtk or gtk-layer-shell to do more then speculate.
In the GTK4 version, the moment the tooltip should be shown, the app has a segmentation fault and instantly stops.
I still need to look at the coredump to see if I can get anything from it.