How can I effectively seal gel stain for a professional finish?

To effectively seal gel stain for a professional finish, apply a clear topcoat such as polyurethane or varnish using a high-quality brush or cloth. Ensure the surface is clean and dry before applying the topcoat, and follow the manufacturer's instructions for drying and curing times. Sand lightly between coats for a smooth finish, and consider applying multiple thin coats for added durability.