All the GTK4 apps I know all exclusive to their specific platforms. Most of them are being made exclusively for GNOME. Some of them have been made exclusively for elementary. I'm not interested if it's technically possible to create DE and WM neutral GTK4 apps. I'm interested if neutral apps are being made, which they aren't, whatever the reasons may be.

I doubt it's a good choice for cross DE and WM apps on Linux, let alone cross platform apps.

Does GTK work for targetting mobile platforms, like your parent wanted?

GTK4 libadwaita has first-class mobile.

https://fosdem.org/2022/schedule/event/mobile_adwaita/

https://thisweek.gnome.org/posts/2022/06/twig-46/

https://aplazas.pages.gitlab.gnome.org/blog/blog/2021/03/31/... (2021)