All it does is measure electrical resistance. How hydrated you are changes how much “fat” it detects. Prove to yourself how useless it is by drinking a few large glasses of water then weighing yourself a bit later. If it’s accurate all that should change is you have the added weight of two glasses of water for a few hours. If your body fat or “muscle” numbers change you’ll know it’s getting you worried about fake news.
The weight loss from a 48hr fast is going to be roughly 1% muscle, 9% fat, and 90% water.
Even if the scale is totally accurate, changes in muscle mass should only be monitored on a biweekly basis - it isn’t volatile enough to be measurably impacted by a normal fast.