Yup. It has a return on one edge which normally forms the front vertical edge of the interior window cill, the return gives rigidity. I think I’ve an offcut in the shed somewhere, I’ll see if I can get a photo.
This kind of stuff. You want the solid foam filled type, not the hollow type. If you go to your local eurocell/Gap/roundband place, they usually have damaged lengths & offcuts to hand for beer money.
https://www.trulypvc.com/roofing/fas...c-fascia-board