"This disk is used for time machine backups" error when installing catalina
I can't select my iMac HD because the OS install believes I am using the same drive for Time Machine backups. I am not - I am using a separate Airport capsule.
I am running OS High Sierra.
I saw another user resolved the problem by finding and deleting backups.backups files on their HD but I can't find such a remnant file.
iMac 27″, macOS 10.13