With decoupling as one important parameter of gauging endurance fitness, I am surprised that Garmin (perhaps others) does not have it as an ongoing parameter to look at during long rides.
On 4-5 hour rides, I keep looking at normalized power to heart rate changes to get a sense.
Their Performance Condition analysis that I have tracked over time is not consistent, and often not in line, with Training Peaks decoupling in the same ride. I have submitted a feedback to them, but if someone with any pull there can get their engineers’ attention, it may make a bigger difference.