Flat earth could say that the sun is getting further away from us and that is why we get that at that angle. When it is closer we can see it over the mountain. We can look at angles to explain this.
Granted as a light source gets further away, we should see the shadow changing shape. Unless someone has a video showing this...
Except we aren't looking at perspective lines. What we are seeing is the shadow being above the object. The only way a shadow appears is for the object to get in the way of the light.
Perspective has nothing to do with this.
The "true path of the sunlight" in that video wouldn't put a shadow on the cloud. It wouldn't illuminate the bottom of the cloud.
And how does he model the sunset?
By having the sun be below Earth, that little block of wood or cardboard or whatever he is using to hide it.
Remember, in the FE model the sun is meant to be some 5000 km high, and at sunset is typically no more than 10 000 km away, with real distances, with the FE model and their fake distances it can get a bit further away.
It doesn't get anywhere near the distance to height ratio shown in the video.