They can all be proven to be bollocks, be it based on an incomplete underatanding of the physics behind it. But usually flat earthers don’t want to listen and just keep repeating the same nonsense to each other.

Edit: here, as reply to those claims in the abstract on that website

• Flat Horizon at High Altitudes:

  • High-altitude photos and footage do show curvature. The curvature becomes more apparent with increased altitude, especially visible from space.

• Horizon Rising to Eye-Level:

  • The horizon does not rise to eye level; it appears lower as altitude increases. This is a perceptual effect due to the vast scale of the Earth.

• Rivers and Canals on a Spinning Ball:

  • Rivers and canals follow the curvature of the Earth, but this curvature is very gentle over short distances. Gravity ensures that water flows downhill, irrespective of Earth’s shape.

• No Detected Movement of Earth:

  • Experiments like the Michelson-Morley experiment and subsequent tests have demonstrated Earth’s motion. Modern technology, such as GPS and satellite communication, relies on and confirms Earth’s rotation and orbit.

• Curvature in Engineering and Construction:

  • Engineering projects account for Earth’s curvature over large distances. For instance, long bridges and tunnels are designed with curvature in mind. Surveying techniques and instruments are specifically calibrated to account for this.