This video clearly illustrates the matter of Soundly's observations on that lake:
Soundly posts this video to show how (some) flat earth advocates (like Ranty) misunderstand refraction.
Ranty posts a video response (Tom's post) demonstrating exactly what Soundly was illustrating.
So that we're all on the same sheet of music...
On a convex surface, refraction bending light down, in the same direction as the curvature, will make the surface appear less curved and even flat or convex if greater than curvature.
On a flat surface, refraction bending light up and away from parallel will make the surface appear curved.
We can all agree on what conditions will refract light and in what direction.
For a flat earth to appear convex due to refraction, air density must increase with elevation to cause the light to bend upward.
For a convex earth to appear flat due to refraction, air density must decrease with elevation at a higher rate than normal to cause light to bend less or not at all.
So which is it? Just showing images of optically wiggling objects isn't analysis. Ranty hasn't refuted anything. He's just exhibited the very behavior Soundly was criticizing.