It's a philosophy not a title https://www.visualscript.com/devops/devops-is-not-a-title-it...

But that still does not align with the use of the word practitioner, it's usually a formal profession with licensing such as medicine or law.

That's just one way to use it. Practitioners practice something. For example you can find https://en.wikipedia.org/wiki/Martial_arts using "practitioner" for people training martial arts. There are practitioners of religion, techniques, etc.