When we see a horizon across from us at 35000 feet above the surface
It is not directly across from us, but below.
Again, this is expected both for reality with a round Earth, and your delusional fantasy.
Nothing more needs to be said on this.
Stop repeating the same pathetic, refuted BS.
Instead, deal with ships on the ocean, and what magic hides the view to the bottom.
Either explain what magic hides the bottom or admit you can't.
Don't bother with pathetic lies like perspective, which we know does not explain it.
Also, don't bother with pathetic vague claims of some magical illusion.
Either explain the illusion, or don't use it.
We’d see that the surface is entirely flat
No, we wouldn't.
Again, you just assert pure BS with no explanation at all and no evidence at all.
Firstly, if you view it just from a fixed position relative to the ship, you just continue to get the same thing, which is what is expected for any smooth surface of constant curvature. That would not allow you to tell if it is flat or round (other than if you viewed it from a point where the bottom was hidden, or just the general observation of a horizon which shows it is round).
If you instead have an observer in a fixed point, then it depends on where that fixed point is, and how accurately you track it.
The simplest one is when the ship touches the horizon at the middle.
In this case you see the ship start behind the horizon, with the bottom obstructed. It then moves along rising up with less and less hidden until it is just above the horizon, with the full above water portion in view, and then it continues moving along, dropping down the other side.
For any other view, you really need to deal with the complex combination of curvature and distance to it, both of which impact the angle of elevation of the boat, and which requires you to carefully track the boat.
e.g. if it starts out at 5 km away (on the horizon), and travels in a straight line, with the distance from you to that line, measured perpendicular to the line, being ~3.54 km, and continues to the horizon at 5 km again, then the bottom of the boat, at the horizon, will be 3.96 m below you, giving an angle of dip of 0.045 degrees (compared to 0.023 degrees for your delusional fantasy). Then when it reaches its closest point at 3.54 km, it will be 2.98 m below you, with an angle of dip of 0.048 degrees (or 0.032 in your delusional fantasy). This is a change of 0.003 degrees for reality and 0.009 for your delusional fantasy.
If you can measure it that accurately, you can just measure the angle of dip to the horizon.
If instead you try to just set up a camera to take the entire FOV, then it will depend on the lens distortion of the camera, which can make a straight line appear to curve up or down.
To get the kind of view you are appealing to, you need an orthogonal view, where you are so far away from Earth, you are in space.
And we have those views, which clearly show Earth is round, so you dismiss them as fake.
You have literally NOTHING to show Earth is flat.
Meanwhile, the simple observation of the bottom of a distant object being hidden from view, obstructed by the horizon, clearly demonstrates beyond any sane doubt that Earth is round.
You refuse to provide an explanation for this, because you know the FE has no explanation.
So instead, you act like the lying, subhuman POS you are, continually attacking the RE with dishonest, pathetic BS; as you know that is your only hope to pretend you are correct.
There’s no great mystery or impossibility to know that Earths surface is entirely flat.
Given you keep asserting this same pathetic BS that it is flat, yet provide no observation or explanation of how that observation makes it flat, it most certainly is impossible.
Given the fact that flat surfaces do not have horizons except the edge of the surface, while curved surfaces do, and we observe horizons in reality, it most certainly is impossible.
Given the fact that flat surfaces cannot obstruct the view to objects above them, while round surfaces can, and we observe this obstruction in reality, it most certainly is impossible.
Just view it from the perpendicular viewpoint of the very same surface
We have been over this before.

The original view is the horizon shown in purple.
The path of the ship is the grey line.
You are trying to appeal to seeing this grey line, from perpendicular to it.
But the view you are trying to use is the blue circle, which has the grey line hidden by the horizon.
To actually view the grey line from perpendicular to it, you need to be basically perpendicular to all of it.
Taking this grey line to be a distance of 10 km, so from the original observer, to the horizon, a distance of 5 km, and an equal distance on the other side; and taking "basically perpendicular" to mean to within 0.1 degree, you need to be 2865 km away
i.e. from space.
We have these views from space.
These views clearly show Earth to be round.
So you need to dismiss them as fake.
You certainly don’t want that viewpoint at all, do you now?
So stop dishonestly appealing to it as if it supports you when it does not.
Again, stop with all the pathetic, dishonest BS, and explain what magic is hiding the bottom.
If you can't, admit you have no explanation and that it is clear evidence that Earth is round.