I've been using a Passport external harddrive to transfer my downloads, then it was being used as a backupdisk for a software update. Unfortunately, every time it's connected to my Mac-book air, it says it's failed. I don't know what else I can do.
MacBook Air 13″, macOS 10.15
If it's failed, the only action is to replace it.
If it's five years old, or older, it should be replaced.
Backups need to be dedicated for that purpose, not used in any dual purpose setup. If you need a drive for data transfer, get a separate one for that. I use a portable 250GB SSD ... PNY by brand name.
Software updates do not need an external drive. The apps are on your main drive. Same for OS updates and upgrades.
My Macbook Air needs backup storage for an update, but my harddrive cannot do it.
