Change light/dark-mode on flutter app via dbus / xdg-portal

with the exception of a few apps I happily use “prefer-dark” for the org.gnome.desktop.interface color-scheme key. The Apps that I have a better time using with bright widgets I prepend “GTK_THEME=Adwaita:light” to ad-hoc or through Exec=. This works for libreoffice and all gtk apps I checked.

Now I’m testing a flutter app that has some images / icons not yet ready for dark mode and this change by env var doesn’t work. Flutter reads settings directly from dbus and I’m unsure what the best approach is to influence it without touching the Apps code and rebuild.

Can I send a command through dbus to the App, or do I need to offer a separate dbus session to an alternative settings store that has prefer-light?