P-brane's video has several flaws.
Let me tell you first about his "without taking observer into account".
I already mentoned sextant and its low price.
(There is even cheaper version that can be made from school protractor, thread, and small hanging object.)
It shows you that angles are measured DIRECTLY FROM THE OBSERVER.
How else you measure those "theta1" and "theta2" here:
https://wiki.tfes.org/Distance_to_the_Sun ?
Next, we do know, or can measure by ourselves angular diameter of the Sun without glare blur around it.
Sun filter will eliminate glare and we will see just the Sun itself.
Sun filter can be simple welding glass or welding mask from Lowe's.
Then measure with caliper.
In P-brane's video it is correctly shown as constant, which ruined his perspective.
Constant Sun covers at close distance just one perspective line, and far away covers 5 perspective lines.
Either lines don't show perspective well, or Sun doesn't follow perspective, which means lines mean nothing.
Next, the speed of the Sun across the sky doesn't depend on observer.
But what observer sees depends on shape of Sun's trajectory.
Sun DOES have constant angular speed across the Earth, traveling around Northern Hub 15 degrees per hour.
Sun also travels 15 degrees per hour in observer's view.
If observer is at Equator Sun can not revolve simultaneously around two points more than revolving radius apart.
If Sun for equinox travels 1670 km/h above equator, it will above equatorial observer at noon travel 15 degrees per hour and at 3 pm 10.5 degrees per hour and at 4:30 pm 7.5 degrees per hour.
Measured directly from observer. Same perspective that reduces apparent height of the sun also reduces traveling segments of Sun's path.
At 7:00 he shows vertical plane in perspective where it is "going away", and green positions of Sun follow,
and another vertical plane left-to right directly in front of us, followed by orange Su positions under some angle relative to previous "going away" plane in perspective.
Projecting those two onto screen will bring them together, but he acts like they are together in 3D in reality.
There's more.