For just cool factor, I was trying to build an elf mage/fighter.
He would be carrying a longsword (NOT rapier), and without versatile, because his other hand needs to be free to cast spells.
I think this is doable in DND5e rules, however, BG3 does not seem to allow that... I am unable to force 1H/2H mode manually.

So even if I take dueling fighting style, the +2 bonus won't apply on the longsword+no shield build... I'd love to see a "fix"