Create new partition or volume on external HDD on Mac mini

I have a Seagate 16 TB external HDD that has a 21 GB ntfs partition that I don't want to lose. I want to create an 11 TB partition or volume (not sure of the correct terminology) on part of the unused space on the drive without destroying the ntfs partition. How can I do this? My external drive is connected to a Mac mini M4 running Tahoe 26.5.