Kleptom is referring to the Shield Master feat in the 5e players handbook. Most feats in 5e have multiple different perks, and shield master actually has three. The shield master feat in BG3 implements only one of these (the +2 to dex saving throws portion).
There are two other abilities with the shield master feat in players handbook. One allows you to use your reaction to take NO damage if you make a dexterity save, rather than half damage, and the other allows you to use your bonus action to shove. Neither of these is implemented in BG3 at the moment, but they are part of the feat in 5e.
