I see older threads asking for this. Garmin WHY do you not support Cronometer? Many people prefer Cronometer over MyFitnessPal for a variety of reasons (I'm speaking of the food tracking - calories). Why not support both Cronometer and MFP??
Based on Cronometer's forums, they are more than happy to work with Garmin so this appears to be something at Garmin's side:
https://forums.cronometer.com/discussion/3019/linking-to-garmin-connect-app