I don't believe Elsa supports bluetooth. If not, you will need an ANT+ dongle. What you linked below would work. Also, does your Macbook Air only have USB C connectors? If so, you will need to get a USB A to USB C adaptor as well: https://www.amazon.com/...aps%2C211&sr=8-2

Yes, you need some way for the ANT+ Quarq elsa to talk to your computer.

You can use an ANT+ stick or you can use a ANT+/Bluetoooth bridge like CABLE which translates all of your ANT+ signals into 1 Bluetooth channel. That way, you don't need a dongle on your computer and you can leave the CABLE bridge by your trainer.

Cable Bridge Explanation:
https://www.youtube.com/watch?v=KcLjXYrtZFQ
-KP