It has not created a new partition.
It has changed the name of the data partition that is created by default by macOS since Catalina. The partition appears as « merged » in the Finder but it separated logically to enforce better protection of the system partition.
This bug with Discovery has been ongoing for months. There are existing threads. Very frustrating.
https://community.wd.com/t/wd-discovery-3-7-214-huge-issues/249660?u=austinforest
