But there is a Db major scale:
https://en.wikipedia.org/wiki/D-flat_major

And a Db minor scale:
https://www.basicmusictheory.com/d-flat-minor-key-signature

These are not shown on the circle of 5ths as they use the enharmonic C# major and minor because rarely is a key signature that uses either a double sharp or flat used today.

FWIW - I use the C# minor scale but I have seen double flats and sharps used in songs:

http://music.stackexchange.com/questions/87/purpose-of-double-sharps-and-double-flats

http://jtauber.com/blog/2006/11/17/why_a-sharp_is_not_b-flat/

When you are at the checkout line and they ask if you found everything say "Why, are you hiding stuff?"

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware