How can I make my bi-fold pantry doors 'look' like a barn door?

Are the doors louvered? You might be able to distress them with paint. If solid, you could do the same, adding rustic hardware, and painting

You could and brackets to back of doors to make each into one door instead of the four door look,that's if I understood you correctly,regardless make it or them into doors that open out. Then I would add hardware that was bold and black in the look and yes the v part that goes on the actual levers won't be able to be screwed in but I would think that as of right now they are held up by just two screws so just glue screw in place. You can also cut out the levers and add a solid piece of wood with more wood in a x pattern to mimic a barn door. If your doors are already solid but have a recessed panel see if you can cut that out if it has curve on top if it's straight then just paint it to look like a barn door not in red and white unless you like that but by using a slight darker color of a wood tone to preserve door until next trend comes. Don't forget to change out handles as well nice big bold black handles. But make sure that you have clearance needed to open the doors out.

If you are going to keep them as bi-fold doors you can create a faux look to the front of them. Cut a sheet of bead board paneling to fit the front of each door and secure with construction adhesive. When cutting the paneling turn your saw on a 15 degree angle and cut thru the board part. That way when the doors are closed the bead board will lap without binding. Trim out the edges with 1 x 4s doing 15 degree angle cuts at seam. To fake the rollers you can attach some lengths of metal strapping (sprayed black) vertically to the top of each door. Attach a roller or a disk of wood (sprayed black) to the top of each piece of metal strapping. Stagger your strapping and rollers so they don't smack together when you open the doors. Paint a piece of wooden lathe black and shim it out and attach it to the wall just below the height of the rollers. NOW ... If you are willing to change out your trim molding around your doors to 1 x 4 or 1 x 6 you could skip trimming out the doors with 1 x 4 except on the bottom. Also you could attach actual roller assemblies to the trim instead of the doors.

Here's an idea to try https://www.lemonslavenderandlaundry.com/bifold-door-faux-barn-door/?utm_medium=social&utm_source=pinterest&utm_campaign=tailwind_tribes&utm_content=tribes&utm_term=281072150_7465584_36641