What is 'Other Volumes'?
A standard macOS startup APFS container does contain additional volumes to the volume with macOS installed on it. You can list these with diskutil apfs list. The standard configuration of such a container is as follows:


disk1s1, the volume you boot from, mounted at /, shown in Disk Utility as Macintosh HD
disk1s2, ‘Preboot’, not mounted, hidden
disk1s3, ‘Recovery’, not mounted, hidden
disk1s4, ‘VM’, mounted at /private/var/vm, hidden


The last 3 are grouped as Other Volumes in Disk Utility. They're required by macOS and shouldn't be removed.