I believe it’s manually spawned in as soon as the animation starts. Attaching the seat to the character could be done with a WeldConstraint and upon the animation ending, the WeldConstraint should be destroyed along with the added seat. I’ve shortly summarized it below.
animation begins>spawn in seat>position seat correctly under player>weld seat to player
animation ends>destroy weld and seat
Of course, this would need a cooldown just so players would not be able to disturb others by spawning and despawning seats, aswell as checks to see if the area you’re trying to spawn the seat in is even suitable for it.
Or you can add a motor6D inside the one of the character’s body parts and set the Part0 as that body part and Part1 being the model that you want to add in