At the moment I'm a happy user of Tredict (https://www.tredict.com/app/). It sits between Garmin Connect and my ChatGPT (they have a ChatGPT connector). Works just great for the training data - in seconds after finishing my training, it's also visible to my ChatGPT, with all the details like intervals, heart rate etc. It's a paid tool, but they offer a 2-month free trial so it's easy to validate for a given use case (and get dependent on it too. :) ).

No, I'm not affiliated with Tredict :) (but if you guys are reading it, good job)