I would assume these events control overall sound for the sim (mute/unmute).
None of these events work in FS2020/2024:
SOUND_OFF
SOUND_ON
SOUND_SET
SOUND_TOGGLE
These events have been mapped to the client:
MapClientEventToSimEvent
Events are sent to FS using:
TransmitClientEvent(hSimConnect, 0, eventID, 0, SIMCONNECT_GROUP_PRIORITY_HIGHEST, SIMCONNECT_EVENT_FLAG_GROUPID_IS_PRIORITY);
All other events work, but not these.