In a most recent Fedora, the following sets the global dbus variable that Google Chrome and Chormium listen on in order to work in dark mode.

gsettings set org.gnome.desktop.interface color-scheme prefer-dark

Without it, `prefers-color-scheme` will always yield 'light' regardless to how you invoke chrome or change its settings. Chrome listens on a dbus variable that is relevant to this gsetting and does nothing else.

To fix this we need to backport two patches in order for it to work in RHEL9. See:

https://gitlab.com/daloni/gsettings-desktop-schemas

https://gitlab.com/daloni/xdg-desktop-portal-gnome

I can open MRs for the two respective repos.