Yeah and “rizz” comes from charisma but isn’t spelled “ris.”
And “OP” has multiple existing potential meanings still in common use today, so it makes sense to me to spell it with flair for the sake of clarity.
Slang is complex and morphs as it travels though; so do some folks use opp as “opponent”? Sure, that’s believable. But I feel fairly confident (never fully confident; I am fallible after all) that it’s original use comes from AAVE and more specifically hip-hop, where I again feel pretty damn confident it refers to an operative and not an opponent.
If I am wrong though, I would love to be corrected (with some verification of some kind) so I can be sure to reconcile the new info and not spread misinformation again. I’ll happily await your evidence to that end.