what is the best external hard drive or external SSD drive to use for time machine

as long as you have the necessary cable, and it is of sufficient capacity, just about any manufacturer's external HDD or SSD will work. you will want a drive the is 2.5 to 3 times (or even more) the capacity of your internal drive. I personally have a Western Digital "my passport" that serves as my TM drive. just make sure to erase and format it before use to remove any preloaded software that supposedly makes the drive "Mac ready" please see Erase and reformat a storage device in Disk Utility on Mac - Apple Support

CarolF5 wrote:

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So, I have an older external drive that does use USB but it is unknown how it will work with the newer Air.

Carol

How old is the hard drive?

FWIW, the backup drive should be the most reliable part of the computer system because if something goes awry the backup needs to be there to recover your data. So, in my opinion, any external HDD that would be older than say 5 years or more, I would not consider reliable.