KDE flatpaks cannot use desktop theme

[1bcb]

 * cinnamon --version
Cinnamon 5.2.7
Not using PPA builds
 * Distribution - Mint 20.3 64-bit Cinnamon
 * Graphics hardware *and* driver used
 `inxi -G
Graphics:  Device-1: Advanced Micro Devices [AMD/ATI] driver: amdgpu v: kernel 
           Display: x11 server: X.Org 1.20.13 driver: amdgpu,ati unloaded: fbdev,modesetting,vesa resolution: 1920x1080~60Hz 
           OpenGL: renderer: AMD RENOIR (DRM 3.41.0 5.13.0-39-generic LLVM 12.0.0) v: 4.6 Mesa 21.2.6`
 * 64 bit

Issue KDE flatpak apps are unable to use the system desktop theme. Attempting to follow the Flatpak documentation's instructions for getting KDE apps to use system themes causes all KDE flatpak apps to break completely.

Steps to reproduce

1)In the settings, change system theme to "Mint-Y-Dark" 2)Install a KDE flatpak app (in this example, KolourPaint) flatpak install flathub org.kde.kolourpaint 3)Install the necessary flatpak theme runtimes flatpak install flathub org.gtk.Gtk3theme.Mint-Y-Dark org.kde.PlatformTheme.QGnomePlatform//5.15-21.08 4)Attempt to run the app flatpak run org.kde.kolourpaint

Expected behaviour Flatpak apps launch and use system dark theme.

Actual behaviour

Flatpak apps using the KDE runtime fail to launch:
flatpak run org.kde.kolourpaint 
Gtk-Message: 19:16:21.557: Failed to load module "xapp-gtk3-module

(kolourpaint:2): GLib-GIO-ERROR **: 19:16:21.581: Settings schema 'org.cinnamon.desktop.interface' is not installed

Other apps using the KDE runtime fail with the same error. For example:

flatpak run com.obsproject.Studio 
Gtk-Message: 19:17:34.582: Failed to load module "xapp-gtk3-module"

(obs:2): GLib-GIO-ERROR **: 19:17:34.605: Settings schema 'org.cinnamon.desktop.interface' is not installed

Flatpak apps that don't use the KDE runtime launch normally (and are able to use the system dark theme).

Other information

I installed a virtual machine of Mint 20.3 MATE and ran the "steps to reproduce," and this issue did not reproduce: the Kolourpaint flatpak was able to launch (although it did not use the system dark theme). For comparison, I also installed a virtual machine of Mint 20.3 Cinnamon and reproduced this issue using the same steps. This information leads me to suspect the issue is specific to Cinnamon.

Searching the internet for information on 'org.cinnamon.desktop.interface' lead me to issue #8239, which the user solved by uninstalling all flatpak apps and flatpak itself and then reinstalling them. I tried uninstalling and reinstalling everything flatpak-related, and it made no difference. And, as mentioned above, I also reproduced this issue on a fresh virtual machine.

I also tried switching the desktop theme to Adwaita-dark and installing org.kde.KStyle.Adwaita//5.15-21.08, and it did not make a difference.

Update 2022 July 14: I installed the Mint 21 beta in a virtual machine on my laptop, and this issue is still present. Here's the system snapshot of my VM:

System:
  Kernel: 5.15.0-41-generic x86_64 bits: 64 compiler: gcc v: 11.2.0 Desktop: Cinnamon 5.4.2
    tk: GTK 3.24.33 dm: LightDM Distro: Linux Mint 21 Vanessa base: Ubuntu 22.04 jammy
Machine:
  Type: Virtualbox System: innotek GmbH product: VirtualBox v: 1.2 serial: <superuser required>
    Chassis: Oracle Corporation type: 1 serial: <superuser required>
  Mobo: Oracle model: VirtualBox v: 1.2 serial: <superuser required> BIOS: innotek GmbH
    v: VirtualBox date: 12/01/2006
Battery:
  ID-1: BAT0 charge: 50.0 Wh (100.0%) condition: 50.0/50.0 Wh (100.0%) volts: 10.0 min: 10.0
    model: innotek 1 serial: N/A status: Full
CPU:
  Info: single core model: 11th Gen Intel Core i5-1135G7 bits: 64 arch: Tiger Lake rev: 1 cache:
    L1: 80 KiB L2: 1.2 MiB L3: 8 MiB
  Speed (MHz): 2419 min/max: N/A core: 1: 2419 bogomips: 4838
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3
Graphics:
  Device-1: VMware SVGA II Adapter driver: vmwgfx v: 2.19.0.0 ports: active: Virtual-1
    empty: Virtual-2, Virtual-3, Virtual-4, Virtual-5, Virtual-6, Virtual-7, Virtual-8
    bus-ID: 00:02.0 chip-ID: 15ad:0405
  Display: x11 server: X.Org v: 1.21.1.3 driver: X: loaded: vmware
    unloaded: fbdev,modesetting,vesa gpu: vmwgfx display-ID: :0 screens: 1
  Screen-1: 0 s-res: 800x600 s-dpi: 96
  Monitor-1: Virtual1 mapped: Virtual-1 res: 800x600 size: N/A
  OpenGL: renderer: llvmpipe (LLVM 13.0.1 256 bits) v: 4.5 Mesa 22.0.1 direct render: Yes
Audio:
  Device-1: Intel 82801AA AC97 Audio vendor: Dell driver: snd_intel8x0 v: kernel bus-ID: 00:05.0
    chip-ID: 8086:2415
  Sound Server-1: ALSA v: k5.15.0-41-generic running: yes
  Sound Server-2: PulseAudio v: 15.99.1 running: yes
  Sound Server-3: PipeWire v: 0.3.48 running: yes
Network:
  Device-1: Intel 82540EM Gigabit Ethernet driver: e1000 v: kernel port: d020 bus-ID: 00:03.0
    chip-ID: 8086:100e
  IF: enp0s3 state: up speed: 1000 Mbps duplex: full mac: <filter>
  Device-2: Intel 82371AB/EB/MB PIIX4 ACPI type: network bridge driver: piix4_smbus v: N/A
    port: N/A bus-ID: 00:07.0 chip-ID: 8086:7113
Drives:
  Local Storage: total: 64 GiB used: 10.53 GiB (16.5%)
  ID-1: /dev/sda vendor: VirtualBox model: VBOX HARDDISK size: 64 GiB speed: 3.0 Gb/s
    serial: <filter>
Partition:
  ID-1: / size: 62.2 GiB used: 10.52 GiB (16.9%) fs: ext4 dev: /dev/sda3
  ID-2: /boot/efi size: 512 MiB used: 5.2 MiB (1.0%) fs: vfat dev: /dev/sda2
Swap:
  ID-1: swap-1 type: file size: 2 GiB used: 0 KiB (0.0%) priority: -2 file: /swapfile
USB:
  Hub-1: 1-0:1 info: Full speed or root hub ports: 12 rev: 1.1 speed: 12 Mb/s chip-ID: 1d6b:0001
  Device-1: 1-1:2 info: VirtualBox USB Tablet type: HID driver: hid-generic,usbhid rev: 1.1
    speed: 12 Mb/s chip-ID: 80ee:0021
Sensors:
  Message: No sensor data found. Is lm-sensors configured?
Repos:
  Packages: 2130 apt: 2121 flatpak: 9
  No active apt repos in: /etc/apt/sources.list
  Active apt repos in: /etc/apt/sources.list.d/official-package-repositories.list
    1: deb http: //packages.linuxmint.com vanessa main upstream import backport
    2: deb http: //archive.ubuntu.com/ubuntu jammy main restricted universe multiverse
    3: deb http: //archive.ubuntu.com/ubuntu jammy-updates main restricted universe multiverse
    4: deb http: //archive.ubuntu.com/ubuntu jammy-backports main restricted universe multiverse
    5: deb http: //security.ubuntu.com/ubuntu/ jammy-security main restricted universe multiverse
Info:
  Processes: 169 Uptime: 1m Memory: 3.83 GiB used: 876 MiB (22.3%) Init: systemd v: 249
  runlevel: 5 Compilers: gcc: 11.2.0 alt: 11 Client: Unknown python3.10 client inxi: 3.3.13

And here's what I get from flatpak commands:

beth@beth-VirtualBox:~$ flatpak list
Name                     Application ID                       Version Branch     Installation
Mesa                     org.freedesktop.Platform.GL.default  21.3.8  21.08      system
openh264                 org.freedesktop.Platform.openh264    2.1.0   2.0        system
Adwaita dark GTK theme   org.gtk.Gtk3theme.Adwaita-dark               3.22       system
Mint-Y Gtk Theme         org.gtk.Gtk3theme.Mint-Y                     3.22       system
Mint-Y-Dark Gtk Theme    org.gtk.Gtk3theme.Mint-Y-Dark                3.22       system
Adwaita theme            org.kde.KStyle.Adwaita                       5.15-21.08 system
KDE Application Platform org.kde.Platform                             5.15-21.08 system
QGnomePlatform           org.kde.PlatformTheme.QGnomePlatform         5.15-21.08 system
KolourPaint              org.kde.kolourpaint                  22.04.3 stable     system
beth@beth-VirtualBox:~$ flatpak run org.kde.kolourpaint 
Gtk-Message: 12:55:22.450: Failed to load module "xapp-gtk3-module"

(kolourpaint:2): GLib-GIO-ERROR **: 12:55:22.521: Settings schema 'org.cinnamon.desktop.interface' is not installed
beth@beth-VirtualBox:~$ 

[FallCheetah7373]

hey there same issue here, no QT flatpak apps respect flatpak themes on mint cinnamon.