These days MongoDB is mostly a subset of what SQL servers do. If all you need is a document store you can simply make a table with a JSONB column and get that. If you later discover you do need relations you can do that with e.g. Postgres but not with MongoDB.

Historically MongoDB has been known for dropping or mangling data in some unfortunate ways, I'm not entirely sure what the story there is these days but personally I wouldn't trust it ever again. Data integrity is too important.