You can use it with no problem. If you want to release a commercial game with UDK, then you’ll need to contact Epic via Unreal Engine (UE5) licensing options - Unreal Engine If they don’t respond after a few days, then maybe we can put you in touch with someone.
I have to ask though… Why are you interested in UDK now? It’s very hard to find support for UDK, it won’t compile for modern consoles, and unless you have a very unusual use case, there are surely better options.