iunno about the Teen Titans. he's about 18 now, sure, but at this point he's been on the Outsiders, helping and teaming up with the pros, and he in college now with his own apartment; Duke has entered or at least should be entering his young adult era. in my opinion he's passed the point of the Teen Titans at this point in his hero career tbh. Teen Titans is more for like sidekick/junior hero types and I feel at this point in his development Duke should be coming into his own as a pro not more junior antics and "learning the ropes". Duke could've/should've joined the Teen Titans earlier, probably during his training era or before he joined the Outsiders. DC missed the boat exploring Duke as a typical teen sidekick hero and now there have been too many "development chapters" for him not to start moving forward in his hero career. that's why I think him on Titans or a Titans-adjacent team are the best options. either that or something like him leading his own Outsiders team, joining like a Justice League branch team, or simply joining a completely new team.
I do like the idea of Avery Ho and Duke being on a team together not that you mention it, and Static would be a great link up too assuming we get a World's Collide crossover event. Naomi/Powerhouse would be a good team-up too but she's also someone who i feel wouldn't be a good fit for the Teen Titans. I think Duke, Avery, and Naomi would be a great foundation for building a Titans team for Duke; Static too if they cross him over.
however, going with your Teen Titan idea, Matt Price from Titans Academy could be the token white boy. he'd complete the team nicely.