As far as I know the only way you can track users' weight is to add them as a connection in Garmin Connect. It would be nice to be able to add people without accounts, underage kids are not allowed to have accounts, and not everyone that want to see their weight stats want and need to have an account.
E.g. I would like to be able to track my kids' and parents' weight, none of them have Garmin Connect account, and they do not need one. It would be nice if I can add people from my account or somewhere in the smart scale memory and be able to access their data from the app without having to login/logout different users. Xiaomi Smart Scale can do this through Mi Fit app, I don't see a reason why this can not be implemented in Garmin Connect.
Also it's not ideal that you can't see all body composition metrics without an account, even smart scales 4-5 times less expensive can display those with minimal input (age, height, gender).