iMac 27" Catalina with Split Fusion Drives I need to have a clean iMac with new OS but experiencing problems.  Having commenced Recovery mode twice with new OS I am seeing Four drives.  One is the 1Tb SSD but the main primary drive is showing as iMac (121.12Gb) plus another two named as iMac2-Data and iMac2-Dat-Dat.  How to have just two drives, SSD plus primary drive?
Here is terminal screen image.
First: it is normal with APFS to list the internal physical drives, followed by 'synthesized' volumes. So you should expect to see /dev/disk0 to 3.
Catalina uses two separate volumes for a system disk: iMac2 is the read-only volume for your OS, and iMac2 - Data is for your apps, user data and everything else.
However, from the looks of it, iMac2 is too small to hold an OS. It looks like you've installed the OS onto iMac2 - Data, and the OS has created a matching  'Data' partition called iMac2 - Data - Data.
I'd suggest erasing the entire device - you may need to check &quot;Show All Devices&quot; in the View menu in Disk Utility - and then install from scratch.