I’m using the minimal edition so I don’t have it installed already.
How the Manjaro Gnome is themed is a combination of packages.
You can find them by looking at the Packages-Desktop definition at Gitlab.
manjaro/gnome/Packages-Desktop · master · Profiles & Settings / iso-profiles · GitLab
Could you please provide an example of an application you think adhere to this theming?
You probably want flatpak-xdg-utils, but I don’t know whether this is what handles the theming.
I’ve got kvantum-manjaro installed already, and I don’t really think I need any other package that’s here, right?
Example please?
Which application are you referring to?
As you have tagged this with Gnome I assume they are default Gnome themed.
Are you expecting the applications to be Qt themed or Gnome themed - I would assume the latter as you are using the Gnome desktop.
dolphin, jDesktopEdit, featherpad, dolphin-emu (when using the native theme style), klevernotes, qownnotes
I don’t understand?
Do you want the Qt applications to use Qt theme on the Gnome desktop?
To be able to better understand your question - I have launched a virtual machine using the latest minimal Gnome ISO.
Then I installed Dolphin using flatpak
The flatpak version of Dolphin is correctly themed using Gnome theming.
I just want flatpak Qt apps to follow the Kvantum theme that is set up OOTB for them, in Manjaro GNOME.
There is not setup any Kvantum theme OOB for flatpak applications.
All users want a consistent theme on the desktop no matter they are mixing the tools Qt and GTK.
You are saying you want the exact opposite?
Kvantum is installed - yes … and native Qt applications will likely use it if configured.
I am sure you can customise you desktop - but if you want the native look of Qt applications you should really use Plasma instead of Gnome.
Neither Manjaro GNOME nor Manjaro Plasma use kvantum out-of-the-box. They use the KDE-default built-in Breeze theme.
kvantum is an SVG-based theme engine intended to offer an alternative to the built-in themes such as Breeze and Plastik.
How do they theme flatpak qt apps then?
Those come preconfigured with the built-in Breeze theme. The only thing that Manjaro adds with regard to theming is the color scheme, which is called Breath, and which is a variant of the Breeze theme.
Oops, I guess I must have forgotten that I had installed the kvantum-manjaro package myself.
So anyway, how do I apply the KvLibadwaita-Maia theme that this package installs to flatpaks?
As I see it the theme is applied as expected to flatpak and native applications.
See the screenshot in above comment
Other than that - I have no idea - I used Gnome many years ago; but I have long forgotten all about it.
The flatpak apps are using the themes provided by the toolkit or the apps themselves (as fallback). I want to use my system Kvantum style on them.
That may not be possible - if you want the apps to follow a Kvantum theme you will most likely need a native application - not a flatpak.
The window layout and decorations, is dictated by the Gnome layout engine - that won’t change.
The following is an example where I replaced flatpak dolphin with repo dolphin - and set a Kvantum theme to showcase
The following is an example where I readded the flatpak version of Dolphin and run it side by side with the native dolphin.
As you can see it will difficult apply a Kvantum theme to your flatpak application unless you do some extensive customisation - and that I cannot help you with.
You would need to use a GTK4 theme matching the Kvantum theme to get a consistent look and feel.
I suggest you search the most popular theme site - pling.com - there is a lot of domain names pointing the same site
The best you could try is by installing flatpak-xdg-utils and then using the GNOME configuration tool (or possibly qt6ct) to force the use of kvantum, but as @linux-aarhus said, I doubt whether it would be possible to force the use of kvantum upon FlatPaks or Snaps, given that they are containerized applications.