Is Arc still being maintained? I understand from reading Manjaro forums previously that the original dev Horst no longer does it, and someone else took over:
https://github.com/NicoHood/arc-theme
Are we getting the theme from the new source for MX19/Buster? Or are we reusing the old Arc theme from Horst?
I ask this because currently in MX15/16 and MX17/18, so long as I install the flatpak version of Arc themes, and I apply Arc (or any Arc-based) theme (even those made in oomox with different colour combinations) on my normal system/desktop, my flatpak apps will follow the theming of my desktop.
But in MX19 Beta, my flatpak app totally ignores my desktop's Arc theme, and shows up in the gnome default Adwaita (light) theme, which I really dislike.
In comparison, flatpak greybird theme is applied if I am using greybird on my desktop.
Could that be also the reason why the XFCE workplace switcher/panel theming isn't so great with Arc?