I use steel sometimes , 2" wood dowels or even wroght iron Mine is 2" wood dowel 14 ft long it was special order from out lovcal Home hardwre it was not expensive really. I have wall to wall drapes on that wall but they are not sure heavy and I just used a hem and put the drpes on the rod with nice hold backs on either side of the large window on that wall. So no need for hradware to hold the drapes . The rod of course needed a center support and finials added to the ends .Have you checked out the sliding panels for your door? Maybe post a pic of your space here in a comment DO NOT start another post.

I have a 20 foot long curtain rod in my bedroom made from plumbing pipe. Most plumbing stores stock iron pipe up to 22 feet long and if you smile they will cut it to length for you. It could be easily spray-painted or I cheated and wrapped mine with the plastic covers made for shower curtain rods, since it was high enough that no one could see the joints.

My husband engineered a 38' long rod for a room with a wall of windows out of electrical conduit. It comes in various diameters. IIRC, we used 1" and spray painted it black.

In order to clear the brackets on this length, we also used "C" rings along with the regular rings.

Initially, I rubbed parrafin wax across the top of the rod to help the rings slide better.