How to give Finn an arc as an actual force user:
On the Star Destroyer, Jannah plugs in the turret but it sparks and then makes a sound like it shuts down.
Close up of Finn closing his eyes.
Reverby dialogue of Finn saying “a feeling…”
The turret powers up and starts firing.
This would likely require a bit of vfx for the Finn close up with eyes closed as there’s not ideal material that would fit right in.