It depends on the design. Some older designs used elastomeric “wipers” that contacted the bullet and degraded accuracy noticeably, though they tended to be very effective at sound reduction when the wipers were new. Such designs are not currently in vougue.
Designs that have no contact with the bullet have very little effect, and in some cases improve accuracy. As the bullet leaves the barrel in a non-suppressed firearm, the gas behind it passes the bullet along with the shock wave of the report. If the end of the barrel (“crown”) isn’t finished exactly square to the bore, then this can disturb the bullet’s flight. Suppressors “catch” this gas and shock wave, and in some cases will improve accuracy. “Compensators” which reduce recoil, but not noise, do a similar thing, and are usually thought NOT to degrade accuracy.
In addition, the loud blast can be a factor in the shooter flinching and throwing off the shot. Cutting down the noise can make an inexperienced shooter quite a bit better. For this reason I always have new shooters wear overkill in terms of ear protection…plugs and muffs both. So I can imagine that not expecting a painfully loud noise probably causes the shooter of a supressed weapon to be a bit better shot…and a lot better if they are not well trained.
Oh, as for the OP: Potatos and pillows do very little to reduce noise.