A stuck Joy-Con SYNC button can be fixed with gentle cleaning and troubleshooting. First, use compressed air to blow dust out from around the button—hold the can 6 inches away and spray short bursts to dislodge debris. If the button is sticky, dampen a cotton swab with isopropyl alcohol (70%) and gently wipe the edges of the button, avoiding getting liquid inside the Joy-Con. Let the Joy-Con dry for 10 minutes, then test the button. If it’s still stuck, reset the Joy-Con by pressing the small reset button on the back (near the USB-C port) with a paperclip for 5 seconds. Reattach the Joy-Con to the console and check if the SYNC button works. If all else fails, the button’s internal switch may be damaged—contact Nintendo Support for repair, as this is often covered under the Joy-Con warranty.