Inconsistent dark theme for GTK apps on 23.04

I have encountered the following issue with using Flatpak apps on Ubuntu 23.04.

Basically, some (parts of) programs will pick up the dark mode I have selected in the settings, while others will not.

For example, here is Firefox: the title bar is correctly themed, the interactive debug thing is correctly themed, but the file picker dialog is not.

Firefox Demo Screenshot

I tried changing gsettings to:

$ gsettings get org.gnome.desktop.interface color-scheme
'prefer-dark'
$ gsettings get org.gnome.desktop.interface gtk-theme
'Yaru-dark'
$ gsettings get org.gnome.desktop.wm.preferences theme
'Yaru-dark'

To no effect. Changing values in the Debug window only affects the title bar, does not affect the file picker.

Setting GTK_THEME=Yaru-dark in Flatseal had no effect.

Running Firefox manually by using

$ flatpak run --command=sh org.mozilla.firefox
[ org.mozilla.firefox ~]$ GTK_THEME=Adwaita:dark firefox

Had no effect.

I have Yaru-dark installed in Flatpak (and it's the only theme I have installed in Flatpak):

$ flatpak list | grep -i gtk3theme
Yaru-dark Gtk Theme     org.gtk.Gtk3theme.Yaru-dark             3.22    system

Did anyone else encounter a similar problem? How could this be solved?

To answer my own question: this is happening due to the Ubuntu version of libadwaita not respecting the light/dark choice.

Here's a lauchpad bug: https://bugs.launchpad.net/ubuntu/+source/libadwaita-1/+bug/2013126

I sent a patch to it, hope it can help

In the meantime, adding ADW_DEBUG_COLOR_SCHEME=prefer-dark to /etc/environment and rebooting should help.