It's no longer an "SDE" that gets created. The current term of art is "Enterprise Geodatabase", and the command to create one is CreateEnterpriseGeodatabase (or EnableEnterpriseGeodatabase, depending on the context). Both of these commands are available in ArcPy, which is accessible with Enterprise.
There is a ".sde" file which can be created, but it is called a "database connection file", and the ArcPy tool for that is CreateDatabaseConnection.
Most of the documentation is geared toward using Pro to administer a EGDB, so going without isn't making it easier, but if you can get to the Python instance in your Server install, you can make forward progress.
- V
