which is best practice for flutter push notifications?

am devloping a chat app with flutter and want to know which is best practice when creating a new room should i create a new topic and subscribe to this topic from the client app , or to use message trigger with devices token using sendtodevice method and sendmulticast

exports.messageTrigger = functions.firestore.document('/Messages/{messageID}').onCreate(
  async (snapshot, context) => {

    var currentRoomUsers = snapshot.data().members;

    
    currentRoomUsers.forEach(  (userID) => {
        db.collection('Users').doc(userID).get().then(async(doc)=>{
        if(doc.exists){
          const message = {
            notification: {
              title: `New message from ${snapshot.data().room}`,
              body: snapshot.data().body
            },
            data: {
              click_action: 'FLUTTER_NOTIFICATION_CLICK'
            },
            tokens: doc.data()['Device_token'],
            android: {
              priority: "high"
            },
            priority: 10
          }

          const response2 = await admin.messaging().sendMulticast(message);
        }else {
          console.log("No such document!");
        }
      }).catch((error)=>{
        console.log("Error getting document:", error);
      });
    
    
    
     
    }
      
      );

i think there is a better way rather than what am actually doing maybe subscribing to topics but how to create a new topic and subscribe users when creating a new room