Some episodes (like The More Things Change: Part 1 & 2 or And Then There Were None/Ben ) are two-part stories that aired together. In season counts, they are still counted as two separate episodes.
On streaming platforms (HBO Max, Amazon, iTunes), the show is often grouped into fewer "volumes" (typically 4 or 5), each containing 16–20 episodes. Do not confuse these with the original broadcast seasons. how many season in ben 10 omniverse