StatusNotifierHostRegistered DBus signal is not allowed, thus broken tray support on KDE Plasma

Sorry I put it wrong. The root of the problem is StatusNotifierHostRegistered DBus signal can’t be passed to snap, despite desktop-legacy slot, so changes to snapd seem needed:

tdesktop already has desktop-legacy slot. The problem is it doesn’t allow StatusNotifierHostRegistered signal. I.e. we need slot to be changed in snapd source code, not to be connected.