There are three answers to this, and I want to hear what the official ruling is. Obviously online games are not counted:
Up To Speed - The last not-online game released for Ben 10. Mobile is a valid market even if most 'gamers' don't recognise it as such. It is officially licensed and even gives us story where the Reboot has left blank. I consider this second-degree canon (i.e. canon until the show says otherwise).
Ben 10 Game Generator 5D - The last full non-mobile non-online game released for Ben 10, and the last game released for the old continuity period. It's crap, it's on PC, and I own it.
Ben 10: Omniverse 2 - The last proper console game. This is only the correct answer if you consider the PC and Console markets to be separate, which they really aren't (excluding counting handhelds like the 3DS or Switch).