On the documentation page for the C# driver, the getting started page is not up to date with the correct method options.
Current documentation
IMongoDatabase database; var bucket = new GridFSBucket(database, new GridFSOptions { BucketName = "videos", ChunkSizeBytes = 1048576, // 1MB WriteConcern = WriteConcern.Majority, ReadPreference = ReadPeference.Secondary });
However, the driver expects a GridFSBucketOptions.