I was having the same problem. I thought it was because camera access was disabled in Settings/Security & Privacy/Camera but even enabling/restarting nothing changed.
Trying to use the pairing code was the same.
I was able to fix it by doing this:
Uninstall Bisq app from your phone and reinstall.
Use the send email with code. Copy/Paste the code and access in your computer. I used Telegram to access the code since I don’t trust email.
Copy the code inside Bisq in your Mac. Wait a few seconds and you’ll receive a notification from the phone app.
If the problem persist, try reinstalling the app again. Every single time the code will be different.