Bearded dragons with the right personality and training can absolutely learn to walk on a leash. It may take a lot of training and patience on the part of a pet parent, but it can be done. In fact, due to their usually calm nature, bearded dragons are some of the easiest lizards to leash train.
First, make sure your beardie is comfortable being held. Next, slowly get them used to wearing the bearded dragon harness. Start with short periods of wearing the harness and slowly increase the time period. When they seem comfortable in the harness, take your bearded dragon to a quiet area outside. Give them time to get used to the new environment. You may need to start with short periods outside until your beardie feels comfortable. Stay away from noisy or busy areas. Finally, try walking slowly using the leash. Let your beardie set the pace, and don’t pull them. If they go the wrong way, block their way and divert them in the right direction.
Always take cues from your pet. If they seem scared or stressed, stop the training for the day. Reward them with treats, like live crickets and roaches, during each session. Some more anxious beardies will never feel comfortable walking. Only continue the training if your pet seems relaxed and interested in the experience.