I assume it's my colorblindness, but on mobile when I move that slider back and forth I just see blue outlines appear around the countries with no other distinguishable changes.
Not the best visualization I should say.
The colors could have been better used to highlight the difference IMO.
For the northern landmasses, Greenland for example, the smaller outline is the equal-earth-projection, and the larger outline is the conventional Mercator projection. That's all there is to it.