How to query for a single field in firestore 9

Question

I am trying to query the doc for data. I found out how to query using the flowing logic

const docRefCol = doc(db, 'UsersCollection', uid);

interface objectData {
   field1Obj: { [key: string]: any };
   field2Arr: [];
 }

 let obj: objectData = { field1Obj: {}, field2Arr: [] };
  await getDoc(docRefCol).then((docSnap) => {
   Object.assign(obj, docSnap.data());  
 });
  
  console.log(obj)

The issue with this is I want an immutable way to extract data. Plus anther way to query for single field (let's say field1Obj), rather than calling the whole document.