Install Fedora33 on 1 of 2 disks

PC has 2 disks, before 2 disks are used by one fedora.
Now I want fedora to use only one disk (the 500 GB disk)
But installation destination wants me to select both disks for installation. When I select only disk (500GB) the installation does not continue.
How to install on only 1 disk?

Did format the second hard disk with mkfs (mkfs /dev/sdb)
That did the trick