Haven't been on jsp in forrrever but I know where to come when I need some pro graphic program insight. What do you usually do when your render has a cut top (straight line) How do you go about blending it?

Nothing?

Find another render. You can't really blend something that isn't there.

Or somehow make it blend with the background, but its honestly not even worth the effort / or won't look good

Can you share what render you're referring to