class ObjectIdAsStringSerializer : SerializerBase<string>
{
    public static readonly ObjectIdAsStringSerializer Instance = new ObjectIdAsStringSerializer();

    public override string Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
        return context.Reader.ReadObjectId().ToString();
    }

    public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, string value)
    {
        context.Writer.WriteObjectId(ObjectId.Parse(value));
    }
}

struct Thing
{
    public string Id { get; set; }
}

[Test]
public async Task test_linq3()
{
    BsonClassMap.RegisterClassMap<Thing>(cm =>
    {
        cm.MapIdProperty(thing => thing.Id)
            .SetSerializer(ObjectIdAsStringSerializer.Instance);
    });

    MongoClientSettings settings = MongoClientSettings.FromConnectionString("mongodb://localhost:27017/?replicaSet=rs0");
    settings.LinqProvider = LinqProvider.V2; // V2 = test passes, V3 = test fails
    var client = new MongoClient(settings);
    string dbName = "testdb-" + Guid.NewGuid();
    IMongoDatabase database = client.GetDatabase(dbName);
    const string id = "590df61373b975210006fcdf";
    IMongoCollection<BsonDocument> coll = database.GetCollection<BsonDocument>("testCollection");
    await coll.InsertOneAsync(BsonDocument.Create(new Dictionary<string, object?>
    {
        ["_id"] = ObjectId.Parse(id)
    }));
    IMongoCollection<Thing> typedColl = database.GetCollection<Thing>("testCollection");
    long count = await typedColl.Find(t => t.Id == id).CountDocumentsAsync();
    await client.DropDatabaseAsync(dbName);
    Assert.That(count, Is.EqualTo(1));
}