I think I found the closest to cannon dark world designs

Art
1

Screenshot_20250819-070158-976
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Could be wrong, but this screenshot is from Spotify. The album is by Toby Fox, called DELTARUNE
PIANO COLLECTIONS: Volume 1.

This could be fanart used, but since the Album is by Toby Fox I think it's fair to assume these are cannon.

Also, cannon Berdly Dark World design.
Was made by the designer of Dark World Berdly.

berdly-art-by-the-person-that-designed-his-dark-world-v0-9tms483zm8e81
berdly-art-by-the-person-that-designed-his-dark-world-v0-9tms483zm8e81650×900 90.9 KB

I don't know if this is already on the Wiki, but I found it somewhere.

2

It’s not an album by Toby Fox, Toby Fox is just credited because his songs were used in the album. The album page doesn’t say who designed the cover, though.

3

Dang.
Spotify listed him as the creator, and as such gave me a notification.

4

Same here