You don't need "thunderbolt".
What you do need is a USB-c external 2.5" drive (either a platter-based HDD, or an SSD).
I'm not sure how many "pre-packaged" HDDs are out there yet that have a USB-c connector. In any case, you could pick up a USB3 drive with a USB-a port on the drive, and use a USB-a to USB-c cable, and it will work fine.
You could also look into something like the Samsung t5 external SSDs. These are very nice, but might not be worth the expense for a TM backup (which doesn't require speed).
You might want to consider TWO external drives:
- one for backups, exclusively
and
- another for media and external storage.
IF money is a consideration, I'd suggest a 2tb external.
Partition it into "two pieces", and use one partition for the TM backup, and the other for "general storage space".
Final thought (on a topic you didn't ask):
I'd consider CarbonCopyCloner or SuperDuper instead of TM.
Either one creates a FULLY BOOTABLE cloned backup that you can boot from in an emergency.
Both are free to download and try out for 30 days.
If you don't like them, just erase the cloned backup and use TM instead.
