What type of lock does MongoDB apply at the document-level?

I’ve been reading the MongoDB documentation for hours, but I couldn’t find a clear and straightforward answer. When updating a document in MongoDB, what type of lock (S, X, IS, IX) does it apply at the document-level ?

In the video I watched, it explains that an S lock is applied to the document during the reading process, and an X lock is applied during the writing process. Is this applicable in MongoDB as well?