Mobx Strict mode warning when updating observable property of object

Question

in my react-native app I use mobx for state management, I just noticed I'm getting a strict mode warning when changing the value of an observable object.

My error:

[MobX] Since strict-mode is enabled, changing (observed) observable values without using an action is not allowed. Tried to modify: [email protected]

How I update mobx state

let copy = userStore.user;
copy.filterMood = 'newValue';
userStore.setUser(copy);

User store

import { makeAutoObservable } from "mobx";
import { makePersistable } from 'mobx-persist-store';

export class UserStore
{

constructor()
    {
        makeAutoObservable(this);
    }
    
    user = false;

    setUser(payload)
    {
        this.user = payload;
    }
}

import { UserStore}  from '../stores/UserStore.js'

export const storesContext = React.createContext({
    userStore: new UserStore()
});

configure({ enforceActions: "observed" });