Overprint and darken doesn't work properly when it doesn't exist a background color.
Illustrator 25.4.1 (64 bit) in Windows 10
When we use darken+overprint in objects that are over some background, we don't have a problem. But if we don't have a background it does the similar to a multiply appearance.
Is there a way to fix this problem?
Please see the photos attached.
I agree that the behavior here looks odd, but only when the black object uses a lowered opacity instead of a tint. I'm not sure what the utility of overprint is in this instance though, or why it would be used in addition to a blending mode.
If you don't use the opacity and instead use tint, or just stay out of overprint preview mode then there's no issue.