Open synced local database when completely offline in electron

After I authenticate and sync my electronapp with my database cluster using MongoDB Realm Sync, I want to open my app completely offline. How can I do that ? It works fine when I open it online. But, when I open it offline, it does not return anything , neither it gives any error.
Below is my code:

    try {
        await app.logIn(new Realm.Credentials.anonymous())
        let config = {
          schema: [DogSchema],
          path: '---path----',
          sync: {
            user: app.currentUser,
            partitionValue: '----partion-value---',
            error: (error) => {
              console.log(, error.message)
        let realm = await
        await realm.write(() => {
          const dog = realm.create('dog', {
            name: `apple ${}`,
            breed: 'labra',
            realm_id: '12345',
            _id: new ObjectID()
        let dogs =  realm.objects('dog')
        // realm.close()
      } catch (error) {
        console.error('create error-->>',error)