Not every episode has to be about something. In fact most of them aren’t, they’re all one-offs. They go to a thing, some problems happen, they solve those problems. It can be thrilling, scary, intriguing, or silly.
None of these grand arc stories where every moment of every episode is so important that if you blink you’ll be lost for the rest of the show. None of these “very special message” episodes either. Just random space adventures most of the time. It worked in the 60s and it’s working today.