Setting an object value inside an atom returns "Cannot assign to read only property 'xxxxx' of object '#<Object>'"

I am trying to edit a key of ‘activeCourse’ inside an object of an atom value. However, whenever i do so it returns the error:

Cannot assign to read only property 'activeCourse' of object '#<Object>'

The atom is called ‘trainingAtom’ and default value is an array of objects:

[
  {
     _id: '5fc42caa244ccadea8e2f263',
     activeCourse: 'r4r3545243j',
     activeDetail: null,
   },
   {
      _id: '5fc42caa244ceecadea8e2f263',
      activeCourse: null,
      activeDetail: null,
    },
]

I am using the following function within my component:

const [test, setTest] = useRecoilState(trainingAtom);

useEffect(() => {
        let _test = [...test];
        const index = _test.findIndex((val) => val._id === id);
        _test[index].activeCourse = 123456;
        setTest(_test);
}, [id]);

This function works if I use normal React state - but anything inside Recoil throws the error.
Note, I have also tried to use the set function inside a selector but it gives the same error.

What am I doing wrong?

[cbuv]

have you tried using updater instead of value? like this:

export const Test = ({id}: any) => {
  const [test, setTest] = useRecoilState(trainingAtom);

  useEffect(() => {
    setTest((old: any) => {
      let _test = [...old];
      const index = _test.findIndex((val) => val._id === id);
      //@ts-ignore
      _test[index].activeCourse = 123456;
      return _test;
    });
  }, [id, setTest]);
  return (<div>{JSON.stringify(test)}</div>);
}

[artygrand]

@drarmstr I trying to use updater as @cbuv suggests, but in my case, I have list of big deep nested objects. For example if I need just to change status in lots[].clients[].bid.status, I have to write like below to defrost whole [lot] object and avoid error

let lots= [...old];

...

let lot = {...lots[x]};
let client = {...lot.clients[y]};
let bid = {...client.bid}
bid.status = val as BidStatus;
client.bid = bid;
lot.clients = [...lot.clients];
lot.clients[y] = client;
lots[x] = lot;

...

return lots;

Should I use dangerouslyAllowMutability or it is possible in any other more simple way?