That would be nice if Garmin Connect added that functionality for those who are working hard at tracking body fat loss. When I was in my cutting phase last spring, I used myfittnesspal.com for this purpose.
If you have any questions, feel free to reach out to me. I have a YouTube channel where I post lots of informative & entertaining videos that talk about running, swimming, and cycling. https://www.youtube.com/watch?v=u3hwFB8-ZuQ&t=226s. Check it out, subscribe if you like, and thanks for your time!