Can't partition external drive

Have been using an external drive with my macbook pro (Mojave), with the name 'Main drive Backup'. Now I want to erase the drive and reformat and partition.. but Disk Utility won't allow me to rename the drive or simply erase the old name, and the option to partition is greyed out, with the only options for reformat as shown.. Even if I erase the drive with new formatting, the partition option is still greyed out and I am stuck with the old drive name?

Where am I going wrong?