Erasing external start up disc
I have a (very) old iMac. It was so slow that I eventually started using an external SSD as the start up drive. I have now moved on to a new system and would like to use the SSD for my Time Machine backups. Sadly, I cannot delete the drive using Disc Utility. Does any one have any advice?
Thank you.
iMac 21.5″ 4K, macOS 13.6