Hi, I have a Scarlett interface and external mic, but Audacity is only reading laptop’s Realtek mic as a selector choice. Mic is plugged to interface, and interface to laptop USB.
Ensure that the Scarlett is plugged in and working before you start Audacity, then select the Scarlett (probably listed as “USB”) as the recording device in the Device Toolbar (https://manual.audacityteam.org/man/device_toolbar.html)