In my playthroughs where I killed it, it didn't land a single hit. It's weakened and hurt. It's easy to climb up and get advantage on your ranged attacks. It's a slaughter.
The one completionist play-through I did, I climbed up above it to attack and it jumped up and absolutely mauled my party! Two characters down.
For most my play throughs I can't justify attacking the owlbear. My wizard thought it too tangential. My paladin balked on moral grounds. Even my pragmatic fighter couldn't justify risk/reward. BG3 is swimming in magic items and has abundant optional fights, can pick and choose.
The trick is to attack and then hide, since it's dark up there. Don't send your whole party. You've got to play strategic. If you do, though, especially with the absolute grunts being distractions... you will steamroll the owlbear. Two or one melee on the floor since they've got the hitpoints at level 3, ranged up.
