How does the Extra Attack class feature impact Two-Weapon Fighting?

Question

A level 11 Fighter makes 3 attacks per Attack action as per:

Extra Attack

Beginning at 11th level, you can attack three times, instead of twice, whenever you take the Attack action on your turn.

According to Players' Handbook, any character can attack with both hands:

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. You don't add your ability modifier to the damage of the bonus attack, unless that modifier is negative.

If a level 11 Fighter is brandishing a light weapon in each hand, how many attacks do they make per turn?

4: 3 from the Attack action + 1 from the bonus action?

Or 6: 3 from the Attack action + 3 from the Bonus action?

Answer 1

Two Weapon Fighting only grants one attack

Two Weapon Fighting does not interact with Extra Attack features. The latter affects exclusively the Attack Action while the former grants an attack as a bonus action.

The Fighter's level 11 Extra Attack feature states:

you can attack three times, instead of twice, whenever you take the Attack action on your turn.

Extra Attack increases the number of attacks you make as a part of the Attack Action.

The rules for two-weapon fighting state:

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.

Two Weapon Fighting gives you the option to make an attack as a Bonus Action when you take the Attack Action.

So a level 11 fighter can make four attacks:

3 attacks from the Attack Action using the level 11 Extra Attack feature
1 attack as a Bonus Action using Two Weapon Fighting.

Answer 2

4 attacks

No matter the number of attacks provided by Extra Attack, you take the Attack action just once. So the number of attacks per action changes, but the number of Attack actions does not.

You have a single bonus action per turn which you can use when you use your single Attack action per turn to make one additional attack.

The exception is, of course, Action Surge, which provides a second action which lets you perform another Attack action but provides no additional bonus action, resulting in 7 attacks total.