I noticed recently (and investigated) problems about Two-Weapon Fightings in BG3
1st: You are suppose to have your modifier on the Attack Roll, yet we do not
2nd: You are not supposed to have your modifier on the Damage roll for Off-Hand attack unless you take the 'Two Weapon Fighting' Fighting Style, yet everyone (even rogues) have their modifier on their Off-Hand damage.
3rd: When you pick the 'Two Weapon Fighting', it adds no damage on your damage roll and does not apply your modifier to your Attack Roll either, so it basically gives you nothing.
I suppose this is either a bug of a mistake, so I felt like it should be reported.