In UAF, it's very clear that Ben lives with his parents, balancing his high school life with being a superhero (as seen in [Grounded]). Even in Omniverse, there are hints that Ben lives with his parents (such as in [Special Delivery], where Ben retreats to his parents' house after wrecking Mr. Baumann's home.
But in Omniverse (and even towards the end of UA as seen in [It's Not Easy Being Gwen]), it appears that he's dropped out of high school to become a full-time Plumber. In [O Mother, Where Art Thou], Ben's mom acts surprised that Ben would come home for dinner. In addition, we hardly ever see Ben inside his house after the end of UA.
Did Ben move out off-screen? If so, it would have to be some time between [Surprise Delivery] and [O Mother, Where Art Thou].