Hi Gibdion,
I found that making “islands” works to get rid of the dark-egde.
I thought I had to make sure it unwrapped in a nice way with connected faces; like the T-shape of a cube (instead of 6 loose squares).
You can see how it worked out for me in this screenshot. The house on the right is a "Smart Unwrap form Blender with a 1.0 dist.) the other is with 2 “connected” sheets (based on seams) with the “manual” Unwrap.
I took the “Blank project” with no assets.
(I have not experimented with (post) light settings