On flat earth the sun is always above the objects therefore it can never cast shadows upwards. Below are real world videos or photos showing shadows being cast upwards by the sun because the sun goes low in the sky on a round earth, which it never does on a flat earth. With a flat earth it is stated that the sun just looks like it sets because of perspective, however the sun actually never goes down so it can't cast a shadow higher then the object on a flat earth.
I hope to make a better video presentation of this. However the idea is sound. We know when we look south that the stars appear to travel clockwise and when we look north stars appear to travel counterclockwise. However on a flat earth no matter where you are the stars will always appear to be moving clockwise because they are directly over head spinning like a fan in comparison to a round earth where stars rotate like a bigger sphere surrounding the a smaller sphere ( the earth ).
Flat earthers will claim this isn't valid because it's a simulation or cgi, however the only way to reproduce a flat earth model is cgi or animation because flat earth is not reality.
In the antartica we have 24 hours of sunlight, which if the earth was flat the sun couldn't light up the whole ice wall at the same time. Now flat earhters will claim antartica doesn't exist and the 24 hour timelapse from Antartica is fake. However those living in the southern most city of South America would also have to be in on the conspiracy as they witness a 24 hour light period as well. Also when we go to Antartica the stars appear to go counter clockwise compared to the North Pole where they appear to go clockwise. This also can not happen on a flat earth.