Harddisk unexpectedly has split into 2 partitions
Hello, I have an iMac from 2017 with OSX Catalina version 10.15.6 with 2 TB drive.
After making a full back-up today, I wanted to make a clean instal of Catalina. Suddenly it appears I do not have 1 harddrive Macintosh HD with 2 TB, but instead I now have 2 MacIntosch HD with each 1 TB and also a nameless partition of 23,55 GB instead of the Macintosh HD Data. All these partitions are full,
so I cannot transfer from one to the other.
When I try to install Catalina it is asking me witch harddrive I want to use. I have spend hours trying to delete 1 of these harddrives but did not succeed. When I try to erase, the procedure is running on the screen but never the less the partitions are still there and are not empty.
How can I return to the situation that all these partitions are again only one?
Gilbert