Changing graphics changes gameplay?

I made a prototype of character movement and a simple enemy. Whenever the character touches the enemy, the character gets knocked back a bit and the enemy is “stunned” for a while. In unity, this works fine. However, when I exported the scene using File>>Build & Run, the knockback velocity is amplified by a lot when the graphics are set to “low” or “very low” when the scene is run (it runs well otherwise).
Why does this happen? Does it have something to do with update or fixedupdate? My scene uses the base assets (simple 2d shapes) and does not have music, pictures, etc. Only scripts and 3 game objects.

in unity , every thing you write in Update() method will work every frame , and if you lower graph settings , it means they will work more often than normal.

work around for this is using : Time.DeltaTime

for example :

this is wrong using scenario : gameObject.Transrom.position.x + = 5

and this is the correct way to write it : gameObject.Transrom.position.x + = 5*Time.DeltaTime