The cantrip Mind Sliver from Tasha’s has a secondary effect applying negative 1D4 to a saving throw.
…subtract 1d4 from the next saving throw it makes before the end of your next turn.
The spell Bane from the Player’s Handbook has a similar effect.
…the target must roll a d4 and subtract the number rolled from the attack roll or saving throw.
Does the effect from Mind Sliver stack with the saving throw effect from Bane making it negative 2D4 to the next saving throw?