I’ve reverse engineered this shower door bracket using the last one that did not break yet. The originals are die cast aluminum, after 20+ years of usage they tend to break. You can get a pair online for $35, but I’ve decided to re-create it from ABS. I’ve altered the geometry slightly to account for the plastic’s lower strength. After printing it’s sanded, primed and painted. I’ve used wood screws to mount it. The towel bars are secured with screws. I've drilled and tapped the holes for them in the bracket. Enjoy!

Print from ABS. Use 90+ % infill. 0.25 mm layer height should be fine. Sand and prime. Paint it to the desired color. Use wood screws to mount to the door. Drill and tap the holes for the towel bar securing screws.