Various GTK4 apps (e.g. gnome-system-monitor, gnome-calculator) don't respect dark mode themes on Fedora 45 Xfce and modern builds of openSUSE Tumbleweed Xfce

Companion issue on GTK's git: https://gitlab.gnome.org/GNOME/gtk/-/work_items/8526

I cannot compile from source so I cannot say for sure when this started occurring, but running GTK4 apps like gnome-system-monitor and gnome-calculator on Xubuntu 26.10 and openSUSE Tumbleweed Xfce build 20260531 generally respect dark mode themes (e.g. Adwaita-dark or Greybird-dark) without issues.

But on Fedora 45 Xfce and modern builds of openSUSE Tumbleweed Xfce, they always insist on using light color scheming in a multitude of GTK4 apps and I've seen this anomaly with gnome-system-monitor, gnome-calculator, and "Mission Center" as well.

Unfortunately I can't say I'm 100% sure what is the commonality here, but it's really easy to test and demonstrate since it occurs even in a live ISO.

EDIT: I swear it used to happen with gnome-disks but I just double-checked and it properly respected the dark theme.

Screenshot showing gnome-calculator on openSUSE Tumbleweed Xfce build 20261028: screenshot

Edited by NM64