[off-topic] remove app association from file extension

[Helmut K. C. Tessarek]

First of all, I'm very sorry to send an off-topic question to this list,
but you are my only hope. discussions.apple.com is utterly useless, the
results I get back from search engines point to outdated, non-working
hacks, and Apple does not reply to questions.
You are after all macOS experts and some of you might even work for Apple.

It's a simple thing really, yet apparently impossible on macOS.

I want to dissociate the file extension .md from any application.
After installing Xcode, the .md extension is associated with Xcode.
Yes, I can change the association to a different application, but I
don't want an association at all.
I want macOS to let me choose the app every time I double click on an
.md file.

Therefore I have this simple question:

How do I dissociate a file extension from an application?

Once again, I'm sorry for this off-topic question.

Cheers,
  K. C.

-- 
regards Helmut K. C. Tessarek              KeyID 0x172380A011EF4944
Key fingerprint = 8A55 70C1 BD85 D34E ADBC 386C 1723 80A0 11EF 4944

/*
   Thou shalt not follow the NULL pointer for chaos and madness
   await thee at its end.
*/

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