Fighter second action

[Darc_Vader]

Clarification from someone with the books in front of them. My group has had it such that -- provided you are holding a weapon in each hand-- you can mix and match with which weapon to make an attack with each of your non-bonus-action attacks. For example, using Chronos example of an action-surging 5th level fighter, it could be 3 swings with one weapon and 2 with the other instead of 4 and 1. Is that rules-supported or did we just decide it made sense?

I am fairly certain you are correct. ‘Main-hand’ and ‘off-hand’ aren’t a thing in the rules; specifically the rules for twf are

Two-Weapon Fighting

When you take the Attack action and Attack with a light melee weapon that you’re holding in one hand, you can use a Bonus Action to Attack with a different light melee weapon that you’re holding in the other hand.

So the only attack pattern that is not allowed is making all of your attacks with the same weapon.