Perhaps there’s a case of parallel development here, but I really don’t think that’s what happened.
Gamer slang has long borrowed, sometimes sincerely sometimes ironically, from AAVE and hip-hop slang, where I truly believe this originates, and clearly has the cop/fed connotation. Yeah, I know people shorthand “opp” as opponent in games in the same way they shorthand everything, but jesus christ that’s more approaching 1337 5p35k customs than gen z/alpha slang, so even if we do assume parallel development and concede opp=opponent in modern gamer slang it almost certainly is pretty unrelated to said archaic use and was likely homespun in zoomer/alpha games like Roblox or Amung Us or whatever they’re playing now instead.
But hey, while I remain unconvinced I am proud to accept my fallibility and ask everyone to remember that I am just some stranger online when weighing the weight of my opinion and to draw your own conclusion on the matter. I do not claim to speak gospel.