Hey,Hi Mutleg,
You should be able to add an analogue audio source without issue. In your scene, add an Audio Input Capture source, choose add new, then select the analogue in. This functionality works on M1.
It's hard to answer for your exact situation as you haven't given many details of your setup. How are you inputting your analogue audio (external recorder or through the MacBook's audio jack)? What is it you're plugging in? Have you tested this setup with another system?