On the oblate spheroid planet, if you walks over the equator you do it in a perfect straight line, zero degrees for any side from that line, never deviate even a tenth of degree, and after 40 thousand km you will find yourself back to your starting point.
On the flat earth model, your walk over the equator is not straight, during the 40 thousand km walk you make a whole 360° turn. If you are walking west, you will make a long right turn to northwest all the time, it will be a 40 thousand km walk, 360°, 111 km per degree, that would be pretty much noticeable and measurable.
===
On the oblate spheroid planet, you can sit down and watch the movement of the stars, anything that raise at the perfect East will set perfectly at West. Anything that raises from Northeast will cross the northern sky, never coming over you, and sets on Northwest. Anything that raises from Southeast, will cross the southern sky, never coming over you, and setting on Southwest.
On the flat earth model, everything on the sky makes a complete 180° turn over you during a 12 hous period of time, nothing will raise or set, things would appear (?) from the Northeast view, make a clockwise 90° turn until it gets right over you, then makes another clockwise 90° turn and disappear (?) over the Northwest, the whole sky is rotating in a circle over you, right?
===
Go outside right after sunset, with a 12" or 30cm ruler, fully extend your arm with the ruler in hand, measure the distance between any two bright stars close to the eastern horizon in the sky that would be around 2 to 5 cm apart. Make note of such measurement. Come back 5 hours later, the same stars will be closer to the top of the sky, make another measurement in the same way, return 5 hours later and measure them almost setting in the western sky horizon. You will have a very important and nice surprise. All the measurements will be exactly the same, to the microns of measurement. I know this experience could not make any sense to most flat earth believers, but it should do. I will explain why. In your flat earth model, the sky is only 3000 miles high and flat, rotating over us. Go to a straight street, put two soda cans 1 meter/yard apart on the walkway, go to the walkway across the street, walks away 50 steps, turn back and walks 100 steps, even being on the other side of the street you will be approaching the soda cans in the middle of the walk. Repeat the ruler measurement with fully extended arm, while you walks, you will notice that the measurement would show a larger number when you will be closer to the cans, right across the street, 90° angle, and smaller when you are at smaller angles and far from the cans.
What conclusion you have with this cans experience? That while you moves on the street, or the street moves on you, objects distances will change while in a lower angle from you, and that distance will be largest while it is right on top of you.
From the 50 steps to one direction and other on the other side of the street and the soda cans, probably you made a 176° of a sweep, triangle of 20 m of height by 100 m of base, your observation distance changed from 20m (across the street) to 54m at 50m away. Your observation of the flat earth sky during horizon to horizon would be 20 thousand km walk (triangle base) to 4.8km high, it will form a triangle with a sweep of 128°, your distance from your sky will be from 4.8km (right on top, 12pm) to 10.1km (at 6am or 6pm), that is more than double the distance, the object size in the sky will be completely different in size. The size formula for different distances is pretty simple, just a ratio. If you see the sun at 12pm as (lets say) 20mm on the sky, at 6pm it will appear as 20 * 4.8 / 11.1 = 8.6mm. But it does not, right? Measure your flat earth sun at noon and at 6pm right before sunset... will see it has exactly the same size. The only explanation is that it is tremendously far away, millions of times further than just 4.8km.
So, why the stars distances are all the same while they cross all your sky? Why they don't change distances from horizon to top of the sky? If you learn any geometry at middle school, you did learn that a 1 meter diameter rotating drum or circle over the ground, the distance from any point on the surface to ground will be a variance from zero to 1 meter, easily measured. If this same drum is lift 10 km up in the sky, now the variation of distance to the ground from any point on the surface of the drum will be a variance from 10000m to 10001m, almost impossible to measure or to notice.
That is the same with stars, they are so far away, several trillions of miles away or much much further, the 6300km difference in distance to the stars of 6 hours Earth rotating 90° will add so little to the total distance, that makes the stars to be at the exact same distance among them. It is the same as in the soda can experience, if you move yourself not just to the other side of the street, but 10 blocks away, and look and measure the soda cans distance through a binoculars, they will be measured the same distance, no matter if you walk 200 yards parallel to them. This is the same effect when traveling by car in the highway, things closer to the road start appearing small at distance, become huge when closer to you, pass fast, reduce size as it distances away. But far away trees and mountains appear to be moving with you at the same size.
When you say the flat earth sky, sun, moon, planets and stars are only 3000 miles (4800 km) high, that is too low for them to keep the same distances when moving all over you through the 20 thousand km half circle of the flat earth equator sky, that is impossible. It is the same as the soda cans across the street, you WILL measure a large difference in distances. Just go outside and measure, you will find none, what proves the spheroid planet.
Oh, too much calculations, numbers and angles for you? Then, sorry, you should not be involved in trying to understand the ins and outs of the scientific world, we call it geometry and astrophysics. I would recommend other areas of interest for you.