Fenix 6 VO2 Max for CYCLING

Hi, I bought my fenix 6 in 2021 and have never been able to get VO2 Max for cycling. I’ve read that I need to record some rides over 20km but it’s never registered for me. So this week I went on 4 rides, all between 30-50km and a still I can’t get a VO2 Max for cycling. Anyone else had this issue and know how to resolve it? Thanks