See https://github.com/mongodb/specifications/blob/b07c26dc40d04ac20349f989db531c9845fdd755/source/server-discovery-and-monitoring/server-discovery-and-monitoring.rst#initial-topologytype

If the directConnection option is not specified, newly developed drivers MUST behave as if it was specified with the false value.

Since changing the starting topology can reasonably be considered a backwards-breaking change, existing drivers SHOULD stage implementation according to semantic versioning guidelines. Specifically, support for the directConnection URI option can be added in a minor release. In a subsequent major release, the default starting topology can be changed to Unknown. Drivers MUST document this in a prior minor release.

In 4.1.0 support for directConnection was added, but we didn't change the default behavior of the driver as required by the spec. We should do it in the next major release.