DevOps should be regarded as an acronym.
An acronym is a word or name formed as an abbreviation from the initial components of a phrase or a word, usually individual letters (as in "NATO" or "laser") and sometimes syllables (as in "Benelux").
The article goes on to talk about mixed-case abbreviations:
Words derived from an acronym by affixing are typically expressed in mixed case, so the root acronym is clear. For example, "pre-WWII politics", "post-NATO world", "DNAase". In some cases a derived acronym may also be expressed in mixed case. For example, "messenger RNA" and "transfer RNA" become "mRNA" and "tRNA".
This, however, doesn’t quite address the particular kind of mixed case you’ve raised, where the initial letter of each constituent word is a capital and the rest are lowercase.
For this, consider the standard abbreviation for Doctor of Philosophy, PhD. Although it’s not an acronym (it’s read as individual letters, not as a single word), it offers support for abbreviations to be written in mixed case. PgDip (postgraduate diploma) is usually pronounced pee-gee-dip, which we might consider to be part initialism, part acronym. It, too, is written in mixed case.
Closer to the mark, we have SoCal, an acronym for Southern California, written in mixed case and pronounced as a word.
So if you treat DevOps as an acronym, mixed case has historical support.