is there a possibility to add the data collected by my Xiaomi Body Composition 2 scale in the Garmin app?
Not sure. You'll have to check. https://www.myfitnesspal.com/
I think I figured out.. MyFitnessPal doesn't sync with MiFit but syncs with Google Fit, so, i have it this way: miFit->Google fit; MyFitnessPal<->Google fit; GarminConnect<->MyFitnessPal
Done!
I still use Strava and sync with MyFitnessPal and GarminConnect, so everything syncs with everything.