When I record something while I have a second track(that isn’t on mute), I can’t hear the track while I record, though I was previously able to.
This started happening after I plugged in a Blue Snowball mic, but I only plugged it in once, and then I stopped using it.
That’s the “host sound system”. The playback device setting is the last dropdown menu on the right end of the Device Toolbar. See: Device Toolbar - Audacity Manual
That’s important.
Look in the Transport menu, near the bottom. Ensure that “overdub” is selected (enabled) and “software playthrough” is not selected (disabled).