Every time I open a new project (without shutting down Audacity completely - "Quit") it comes up with an error message

So this is not preventing you from recording. Good.

Make sure that Audacity has access to the “microphone”. See https://forum.audacityteam.org/t/no-recording-level/51788/1

Set the Audacity recording device to the internal microphone.

What happens now?

– Bil