In one of Techtives shorts, he says suppressors will have a negative impact on bullet velocity.
But in reality, suppressors generally increase muzzle velocity from any where from +10 to +60 FPS.
Suppressors do require more cleaning more often as well as making it heavier effecting ADS.
If a negative impact is needed for suppressors, this is it.
https://www.silencershop.com/blog/do-suppressors-increase-velocity