I don't know what you studied in your education, but it's plain that science is not your strong point. Light travels around 150 km from the sun to the earth. Stars are vastly further away. Light is just a higher frequency on the electromagnetic spectrum. The distance it travels depends entirely on the power of the light source.
Your "fairly sure" is in fact the opposite. Radar definitely is evidence that the earth is a globe.
I did some quick research, else this is ever going to be a stalemate.
https://www.quora.com/What-is-the-range-of-an-average-marine-radar-on-US-Navy-ships?share=1
It sounds like a typical, off-the-shelf military radar has a range of about 25 nautical miles (although some have much further range). I believe 25 nautical miles translates to 46.3 km.
Presuming the radar is mounted 10 m above the water (I think this is conservative, as lots of boats would be shorter), and the boat it is detecting is 10 m above the water, the maximum distance the radar could detect this boat on a ball-Earth is 24.79 km.
Just enter the heights of the observer and object in the calculation page attached.
https://rechneronline.de/sehwinkel/distance-horizon.php
So, ball-Earth theory predicts a maximum radar range for this scenario of 24.79 km, due to curvature of Earth, but a standard radar (probably mounted much lower) can detect up to 46.3 km. Bear also in mind even more powerful radars can purportedly achieve better range, trashing ball-Earth theory even further.
As I indicated previously and suspected it would be, marine radar is a proof/verification of the Flat-Earth we observe, and a refutation of Ball-Earth theory.