The Connect IQ simulator is awesome because it allows you to iterate/test quickly. It appears that there might be a bug with pairing an ANT+ sensor to the Connect IQ simulator when you are running on Mac.
I have tried both the Connect IQ 8.1.0 and Connect IQ 7.4.3 sdk versions, and with both I was unsuccessful at detecting nearby ANT+ sensors.
I tried using a Garmin Varia and I tried broadcasting HR from my Garmin Forerunner 955.
I am using a SUUNTO ANT+ dongle that works on my mac with Zwift (I am able to pair my broadcasted HR from my watch to the dongle when I use Zwift).
I have done some troubleshooting with Claude and was unable to get it working. I verified that Garmin Express is not running; and that Zwift is not running. I verified that my mac can see the USB ANT+ dongle from the terminal. I tried all usb ports on my Mac to see if that was the issue.
We already have some discussion on this issue here: https://forums.garmin.com/developer/connect-iq/f/discussion/305745/how-to-connect-antplus-sensor-to-the-simulator/1918779#1918779