Seeing Polaris and Southern Cross

If the Earth is flat .:
(1) Why can't you see the Southern Cross in Alaska or Canada ?
(3) Why can't you see Polaris in Sydney or Johannesburg  ?

Their lights are blocked by the earth's surface because the flat earth is traveling >> Downwards Universal Deceleration AKA DUD (the better version of Universal Acceleration).

1. The stars' lights go downwards (while go other directions) by velocity while the earth goes downwards by deceleration.
2. By DUD model, the air (which relatively resembles the earth's deceleration) will hit the stars' lights somewhat upwards. So it needs more height to see those stars.

Their lights are blocked by the earth's surface because the flat earth is traveling >> Downwards Universal Deceleration AKA DUD (the better version of Universal Acceleration).

1. The stars' lights go downwards (while go other directions) by velocity while the earth goes downwards by deceleration.
2. By DUD model, the air (which relatively resembles the earth's deceleration) will hit the stars' lights somewhat upwards. So it needs more height to see those stars.

I'm not seeing an upward/downward movement, just a rotation. In this video, the user sets the equatorial mount as fixed on the night sky (Southern Cross, in this case):

Their lights are blocked by the earth's surface because the flat earth is traveling >> Downwards Universal Deceleration AKA DUD (the better version of Universal Acceleration).

Try to draw a diagram. If you do, you will see that bends light in the wrong direction.

If the light initially heads out "horizontally" relative to us, the acceleration (which you call downwards deceleration) would results in the light bending down relative to us.
This would make celestial objects appear higher, not lower.