Birgi after fetching with Fireflux Squad doesn't work.

[Beroestheenvoy]

I attacked with Fireflux Squad and exiled another creature with its trigger and got Birgi. Next turn when I cast spells there was no trigger to acquire red mana for each spell cast.

[Alex-Vasile]

[[Fireflux Squad]], [[Birgi, God of Storytelling]]

[github-actions]

Fireflux Squad - (Gatherer) (Scryfall) (EDHREC)

{3}{R}
Creature — Human Soldier
4/3
Haste
Whenever Fireflux Squad attacks, you may exile another target attacking creature you control. If you do, reveal cards from the top of your library until you reveal a creature card. Put that card onto the battlefield tapped and attacking and the rest on the bottom of your library in a random order.

Birgi, God of Storytelling // Harnfel, Horn of Bounty - (Gatherer) (Scryfall) (EDHREC)

{2}{R}
Legendary Creature — God
3/3
Whenever you cast a spell, add {R}. Until end of turn, you don't lose this mana as steps and phases end.
Creatures you control can boast twice during each of your turns rather than once.
🔄
{4}{R}
Legendary Artifact
Discard a card: Exile the top two cards of your library. You may play those cards this turn.