Does Absorb Elements' additional 1d6 get doubled on a critical hit?

Question

Absorb Elements, as part of its effects, has this line.

[T]he first time you hit with a melee attack on your next turn, the target takes an extra 1d6 damage of the triggering type, and the spell ends.

But what happens if you score a critical hit?

When you score a critical hit, you get to roll extra dice for the attack's damage against the target. Roll all of the attack's damage dice twice and add them together.

Is that extra 1d6 considered part of the attack, and thus rolled again? My gut says yes, but I cannot think of any explicit rule that says so

Answer 1

You quoted the related rules about Critical Hits: let's have a look have them with some insights (emphasis mine):

When you score a critical hit, you get to roll extra dice for the attack's damage against the target. Roll all of the attack's damage dice twice and add them together. Then add any relevant modifiers as normal. To speed up play, you can roll all the damage dice at once.

For example, if you score a critical hit with a dagger, roll 2d4 for the damage, rather than 1d4, and then add your relevant ability modifier. If the attack involves other damage dice, such as from the rogue's Sneak Attack feature, you roll those dice twice as well.

Absorb Elements lets you add an extra 1d6 damage die: it is part of the damage dealt with the attack, hence you apply the rule bolded in the first paragraph. Furthermore, the second paragraph contains an example that clarifies what happens when the attack involves additional damage dice.