Time Machine destroyed a new external hard drive and failed to back up in process
How can I restore or recover a new hard drive that is now unreadable by MacBook?
MacBook Pro 15″, macOS 10.12
Perhaps the chosen external drive may have been defective.
These could be that way; when new, or if seldom used.
• Backup disks you can use with Time Machine - Apple Support
https://support.apple.com/en-us/HT202784
• Time Machine troubleshooting on Mac - Apple Support [catalina]
https://support.apple.com/guide/mac-help/time-machine-troubleshooting-mh15653/10.15/mac/10.15
• above article except link shows prior macOS 10.13 instructions:
https://support.apple.com/guide/mac-help/time-machine-troubleshooting-mh15653/10.13/mac/10.13
• macOS Big Sur: Using APFS on a Time Machine drive has some catches.. | macworld
• Apple OSX and Time Machine Tips | J. Pond (©2013 Archive)
http://oldtoad.net/pondini.org/OSX/Home.html
Not sure what the default format may have been, if your Mac runs newer than High Sierra.
The hardware inside your Mac could dictate the format for external Time Machine USB.
There are various articles that offer ideas on mac sites.