5e rules say that if a weapon has the
Thrown property, then it can be used to make a ranged attack, so it feels to me as though if a character has the ability to make multiple (ranged) attacks a turn then they should be able to make them with thrown weapons.
If something isn't a weapon with the Thrown property, then as far as I can tell (though I'm no expert on 5e), it isn't judged to be making a ranged attack when thrown so falls under different rules. Throwing a
bomb, for example, is defined as taking an action rather than being an attack.
If that's right and were implemented into BG3 then characters with extra attack would be able to make multiple thrown ranged weapon attacks per turn but goblins wouldn't be able to chuck multiple bombs. But this would mean handling throwing for Thrown weapons differently in the engine than throwing generally.
I confess I've never tried using extra attack with thrown weapons, but I assume from the OP that it doesn't currently work like that?