The posterboard app only works in iPadOS 16 beta 1 and it’s no longer avaliable so iPadOS 17 fixed this problem. Models compatible with ipadOS 17:
- iPad Mini (5th Gen or later)
- iPad (6th Gen or later)
- iPad Air (3rd Gen or later)
- iPad Pro 10.5 inch
- iPad Pro 12.9 inch (2nd Gen or later)
- iPad Pro 11 inch (All generations)