The recent LakeCTF onsite finals had exactly that. LLM usage was forbidden (but players still used their own devices) and there were real-life challenges such as lockpicking as well. I’m part of the organizer team and what we’ve heard so far from participants was that it was really enjoyable not to have any LLM help because suddenly the actual skill and thrill when solving a challenge mattered again. I think what helped in this case as well was that the prizes weren’t high-value enough to incentivize cheating but that participating in the event itself and the social aspect around it are the main point.