They could make this canon under a parallel timeline. Wouldn’t be far fetched to say the timeline could have split when bobidi was killed by buu.he is a magical being and his death could have cause a split in the timeline. Let’s say the events of the buu saga happen exactly the same in both timelines. But things went different after the buu saga ended. Suppose goku decided not to train uub right off the bat and is waiting till he’s older in super. Would explain why he’s not a part of super yet. We all know that he was just forgotten about but there’s a whole other story just waiting to be written. Uub can still make his comeback