Rest and Recovery Apps
Either you can buy a collection of casios that each have different functions or you can download apps that have a niche purpose. I have been playing with Gentler Streak and Training day. One looks at heart rate and training. The second looks at resting heart rate and heart rate recovery.
According to the Gentler streak app my fitness “seems stable”. It looks at the routine over the last few months and years, and by this metric decides whether fitness is increasing, stable or declining.