Oh, actually this could be added to the Shield Master Feat.
RAW, Shield Master allows you to use bonus actions to Shove enemies. However, in BG3 you can already do this, making the Shield Master Feat less useful.
So, Larian could change Shield Master to work more like what you suggested @Tomo: "While wielding a shield and a one-handed [piercing?] weapon and a melee attack misses you, you can use your reaction to make an opportunity attack." Something like that
