Hi Oscar
If you are coming to France from abroad… you will more than likely be walking through metal detectors at some point just to arrive on French soil.
The metal detectors are in place for a very good reason and ordinary folk (such as you and I) may consider them a nuisance and/or embarrassment (at times) but we all know why they are there.
You intend to travel widely, across France… and frankly, it is not possible for us (or anyone) to say with hand on heart where you will or will not come across a metal detector.
Have you thought of asking your friends … here in France… what is currently in place around them… in Paris, Bordeaux etc etc… since you are planning to visit them it might ease your mind to have their help and support.
the borders are not yet open… you have plenty of time…