Yesterday I got flu with high temperature. I feel by myself that I breathe harder and more often.
Garmin tracked no change in my respiratory rate compared to my baseline.
Oura Ring tracked +2.1 breath per minute change compared to baseline.
Here is other since based fresh review of Garmin's unreliable data for Respiratory Rate - http://www.muscleoxygentraining.com/2022/09/respiratory-rate-metrics-ecg-vs-hrv.html
I suppose that this topic will be a point for improvement for Garmin.