The FET doesnt seem to account for seasons, how would flat earth get Spring, Summer, Fall and Winter?
That is literally explained in the FAQ.
I mean, they don't have any explanation for how that works - what force makes the sun go in a circle or makes the diameter of that circle keep changing, what makes the sun speed up and slow down so that the day length remains constant (by 'day' I mean the day/night cycle, of course), if the diameter of the sun's circling keeps changing then the sun would have to be travelling faster when the diameter is biggest and slower when it's smallest.
They have no actual explanation for how any of that
works, but that is their explanation.