The reason we can know when the sun will rise and set is because it has happened before, and is reliably periodic.
Then show how you determine sunrise and sunset without a formula that requires a round Earth. Demonstrate that you are right. Should be easy.
You won't because you can't.
So you believe
It's a fact.
Fortunately, you can test it yourself.
https://en.m.wikipedia.org/wiki/Sunrise_equation
All you need are charts.
Show those charts.
If it's cyclic then there must be a formula to calculate it. Do you know a formula that does not require a round earth?
because the formula are built from (and in accordance with) the real observations
Correct, and the observation is that the Earth is round and rotates 15 degrees per hour. Without that part, the formula doesn't work.
If the Earth is flat, why does the formula work?
Why can you not produce these "charts" that you claim exist or a formula that doesn't require the Earth to be round?
Apart from that agreement, what else did the Naxis do that was bad?