Anadi el collection users para que collection Threads sea una sub coleccion.

screens/main/Home_page.js

 export function Home_page({navigation}) {
   const [threads, setThreads] = useState([]);  
   const [loading, setLoading] = useState(true);
+  
+  //const [roomName, setRoomName] = useState('');
+  //const navigation = useNavigation();
 
   useEffect(() => {
 
     const fire = firebase.firestore()
+    .collection('Users')
+    .doc(firebase.auth().currentUser.uid)
     .collection('THREADS')
     
     .onSnapshot(querySnapshot => {
   if (loading) {
     return <Loading />;
   }
+
+
+  /*function handleButtonPress() {
+    if (roomName.length > 0) {
+      firebase.firestore()
+        .collection('Users')
+        .doc(firebase.auth().currentUser.uid)
+        .collection('THREADS')
+        .add({
+          name: roomName
+        })
+        .then(() => {
+          navigation.navigate('allChats');
+         });
+    }
+  }*/
+
+
+
+
+
   
   return (
     <View>