On CachyOS with KDE Plasma 6.5.5, after updating OpenDeck to v2.9.0, hiding the tray icon with Plasma's System Tray Settings initially works, but any system restart/reboot will cause the tray icon to be visible again.
Potential causes could include some form of icon/app id being detected as a "new" app (some randomly generated id?). Issue only occurs with OpenDeck, and only after v2.9.0.