watch is not collecting cardio fitness data

Remember not all exercises count VO2Max

Make sure the your personal information is up to date in the health App.

Height, weight, age, sex

Then reset your fitness calibration data

From your iPhone>Watch>Privacy>Reset Fitness Calibration Data>Tap this

You will just get a confirmation box that tells you that your metrics will not be as good if you do this.

Tap confirm and do it. You will get nothing else, no confirmation but it is done.

Then go for a 20 minute outdoor run or walk using the workout app at your normal speed on a flat road/path etc

This will re-calibrate the watch.

Not this time but the next exercise that calculates VO2Max it should work.

To measure Vo2Max you must do an outdoor walk or run and hiking,no other workouts will measure vo2max.