AppImage hardware media buttons does not seem to work / no media controls

[sunjerry019]

System information

System
Platform: Linux
Distro: AlmaLinux 9.4
DE: KDE Plasma 5.27.11 / KDE Frameworks 5.115.0 on X11

This issue has also been reproduced on:
Platform: Linux
Distro: Arch Linux
DE: GNOME 46 on X11

App Version
AppImage, spotify-qt v3.11
Built using Qt 6.6.1
Commit 83bfc5d
Built on Dec 31 2023

Backend: librespot 0.4.2 installed via flatpak

Output from spotify-qt

ABI             : x86_64-little_endian-lp64
App version     : v3.11 (83bfc5df)
Build type      : Release
Current desktop : KDE
D-Bus support   : Yes
Device          : spotify-qt (librespot) (Speaker)
KCrash support  : No
Kernel          : linux 5.14.0-427.22.1.el9_4.x86_64
Keychain support: Yes
Platform        : xcb
Product         : AlmaLinux 9.4 (Seafoam Ocelot)
Qt version      : 6.6.1

Detailed information

Hardware media buttons do not work. The DE also doesn't seem to realize that spotify-qt is playing media that could be paused/played/...

Could be related to #119

What happens?

After starting to play, hardware buttons for "Play/Pause", "Next" and "Previous" do not cause any change in spotify-qt (no reaction at all), whether inside or outside the window. Application logs and Spotify logs also do not show anything when the hardware buttons are pressed.

As a further sign, playing a song in spotify-qt doesn't show media control buttons, only volume control:

xev shows that the hardware button is indeed seen by the system:

...
KeymapNotify event, serial 43, synthetic NO, window 0x0,
    keys:  2   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   
           0   0   0   0   0   16  0   0   0   0   0   0   0   0   0   0   

KeyRelease event, serial 43, synthetic NO, window 0x6000001,
    root 0x278, subw 0x0, time 272640855, (-353,73), root:(838,694),
    state 0x2010, keycode 172 (keysym 0x1008ff14, XF86AudioPlay), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

MappingNotify event, serial 43, synthetic NO, window 0x0,
    request MappingKeyboard, first_keycode 8, count 248
...

What should happen?

Hardware media control buttons should work, and media control buttons should be available.

For example, playing the same song through Firefox/Spotify Web shows this:

Thanks for looking into this!