No tray icon in KDE-Plasma 5.26.5

[flix 0]

Hi,

when I select the option Edit → Preferences → Minimize to system tray and minimize the window, there is no tray icon.

I have reset my KDE taskbar to default settings with no luck. All my other tray icons (e.g. Dropbox, Nextcloud) are shown.

My system:
Synergy-Version: synergy_1.14.6-snapshot.88fdd263.flatpak
KDE-Plasma-Version: 5.26.5
KDE-Frameworks-Version: 5.102.0
Qt-Version: 5.15.8
Kernel-Version: 5.15.91-1-MANJARO (64-bit)
Grafik-Plattform: X11

Thanks in advance, regards,
Flix