>>16707801
The force on the scale from the two weights totals 200 N. But the reading is 100 N.

Scales are meant to be used while stationary. I.e while the force holding the scale is equal to the force weighing it down. Doesn’t matter if the force holding the scale is your hand, or a rope attached to a wall, or an object of equal weight.
Use picrel and you will understand.