Someone using a wheelchair approaches on the path and your dog barks. The person needs a safe, unobstructed way through. Move your dog aside or turn away early, do not ask the person to stop, explain their device, or serve as a training partner.
A dog can find unfamiliar shapes, motion, or sounds startling. That does not tell you anything about the person they are reacting to. Keep your dog on a secure lead, choose wider paths while you work on this, and reward calm passes at a distance. If your dog lunges or may reach someone, get help from a qualified, reward-based behavior professional before practicing near the public.
Practice off the path
If you have access to a mobility aid and a consenting helper, start with it stationary at a comfortable distance in a private, safe place. Reward your dog for noticing it while remaining loose and able to move away. Then, only if that is easy, add a small amount of movement. Increase one dimension at a time: distance, motion, or duration. Do not use someone else's necessary equipment without permission, and never obstruct an aid or its user.
On real walks, use a practiced "this way" turn before your dog becomes tense. If they freeze, refuse food, or bark, you are too close for learning. Give more space next time. A safe pass without greeting or investigation is enough.
If the reaction started suddenly or has spread to many ordinary objects, ask your veterinarian about health or sensory changes. Your goal is not for a stranger to prove that their wheelchair is harmless. It is for your dog to feel comfortable enough to let them pass. For more on moving past unfamiliar sights calmly, see the reactive-walks guide. Wheelchair and walker users must not become training partners without their consent.
Sources: Humane Society of Sonoma County: Desensitization. Dogs Trust: How to understand your dog's body language.