IMO the best way to handle difficulty in BG3 is to use the table in the DMG on page 82. There is an xp threshold for easy, medium, hard, and deadly along with an encounter multiplier to take into account the number of monsters and the multiplier that would have on total xp and, in turn, the total CR of the fight. I personally don't like the idea of just buffing all monsters on harder difficulty because that kind of defeats the purpose of the monster. For example, in nearly all cases, goblins/kobolds,etc are used as fodder. If you pump up the difficulty, I wouldn't want to see ogre-d out goblins with 30hp, I'd rather see maybe larger groups with other monsters added in that fit the story. Orcs, worgs, ogres, goblin shaman, all work great with goblins and add to the overall CR. I also realize they can't just go from an easy difficulty with a group of 3 goblins to a deadly difficulty with 20 goblins because of physical restraints, like the size of the cavern/room/cave/etc, but adding in higher CR monsters without messing with their stats is a better way to go so you still keep the feeling of D&D where goblins, for example, are supposed to feel like fodder most of the time but, in groups, can still be deadly. I get that it might be difficult to do in a game but I really hope that, if they do have different difficulty setting, they don't mess with monster stats too much.
