We have a new MacBook Air with a USB4 port that we'd like to connect and transfer all the files from our old computer a MacBook Air 13 inch 2017 (which has a USB A and I think an original thunderbolt port.
Are you asking how to make a Thunderbolt connection, or a USB one?
If you are planning to back up your old computer to an external drive (Time Machine, Carbon Copy Cloner clone backup, or SuperDuper! backup), and migrate from the external drive, then what you would want is some sort of USB-C adapter. There are many options for doing this, but here's one.
Other options (like a USB-C or Thunderbolt dock, or a simple USB-A hub with a USB-C cable) might offer more ports in return for tying up one of your two USB4 (Thunderbolt) ports.
If you are planning on migrating using a wired connection from one computer to another, I believe that you might need to use a Thunderbolt connection.
Transfer files between two Mac computers using target disk mode - Apple Support
If it had to be Thunderbolt, you'd need a $50 Apple Thunderbolt 3-to-2 adapter and a $30 Thunderbolt 1/2 cable. Unless you expected to be connecting the two machines a lot, I think that your money would be better spent on an external hard drive (which you could use to do the transfer, then re-purpose and use as a backup drive for the new machine).
Are you asking how to make a Thunderbolt connection, or a USB one?
If you are planning to back up your old computer to an external drive (Time Machine, Carbon Copy Cloner clone backup, or SuperDuper! backup), and migrate from the external drive, then what you would want is some sort of USB-C adapter. There are many options for doing this, but here's one.
Other options (like a USB-C or Thunderbolt dock, or a simple USB-A hub with a USB-C cable) might offer more ports in return for tying up one of your two USB4 (Thunderbolt) ports.
If you are planning on migrating using a wired connection from one computer to another, I believe that you might need to use a Thunderbolt connection.
Transfer files between two Mac computers using target disk mode - Apple Support
If it had to be Thunderbolt, you'd need a $50 Apple Thunderbolt 3-to-2 adapter and a $30 Thunderbolt 1/2 cable. Unless you expected to be connecting the two machines a lot, I think that your money would be better spent on an external hard drive (which you could use to do the transfer, then re-purpose and use as a backup drive for the new machine).
Apple has a Thunderbolt 3<-->Thunderbolt 2 adapter: Apple Thunderbolt 3-2 Adapter
You'd also need a Thunderbolt 2 cable like this one: Thunderbolt 2 Cable From Amazon
While the above cables would provide a fast way to migrate from your old Mac to the new one, they also require nearly $100 to purchase them.
Unless you'd have additional needs for the adapter/cable, I'd recommend going with Servant of Cats recommendation and, instead of investing in the adapter/cable, invest in an external drive. That way, you'd only need the adapter he linked to.
Adaptor to connect a thunderbolt 4/USB 4 to a USBA - does that exists?
