question

When the "lobby host" creates a matchmaking ticket, what event can I do to share ticketID to all lobby members?

Sorry for the late reply, lobby owner can share matchmaking tickets with other lobby members through lobby data.

After that, only the "lobby host" can receive the event from PlayFabMultiplayer.OnMatchmakingTicketStatusChanged, the other members do not know anything about their ticket status, is it a rule or I do something wrong?

From my testing, other members (those who join the ticket created by lobby host) can also receive the OnMatchmakingTicketStatusChanged event. For more info, you can refer to my example code below:

 PlayFabMultiplayer.OnMatchmakingTicketStatusChanged += PlayFabMultiplayer_OnMatchmakingTicketStatusChanged;
    
 private void PlayFabMultiplayer_OnMatchmakingTicketStatusChanged(MatchmakingTicket ticket)
     {
         // Store and print matchmaking ticket
         Debug.Log(ticket.TicketId);
    
         // Examine matchmaking ticket status
         Debug.Log(ticket.Status);
    
     }