It is depending where and when you are weighted in my experience in France.
At a mandatory examination like a job physical examination or at a volontarily examination which took place at a medical center for a routine complete check up every two years or less frequently like it is now since a few years every five years, I have been always weigthed in underwear after undressing in a small locker room
At mandatory school physical examination a long time ago, it was in underwear or stark naked
For military service at draft physical examination and induction physical examination, it was always in the nude
And at a private doctor'office for an appointment, it was either bare chest or still completely dressed except shoes