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/


I think my wife has started to show the first signs of dementia.
She said she can't remember what she ever saw in me!

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