A report from iPhoneSoft recently mentioned that the 5th-generation iPad and the 1st-generation iPad Pro models will be left out of iPadOS 17 support when it launches.

Apple occasionally drops older devices from future operating system updates. This time, the iPadOS 17 may not be arriving to the 9.7-inch and 12.9-inch iPad Pro, as well as the fifth-generation iPad. Hardware specs reveal that the iPad Pro uses the A9X chip while the iPad uses the A9 chip- Apple dropped support for the iPhone 6S with iOS 16, which shares the same processor.
There were also claims that Apple will drop support for the A11 Bionic, but this isn’t the case. That said, the iPhone X and iPhone 8 models will be safe for now. Though the iPad Pro and iPad won’t be getting iPadOS 17, the devices can still receive updates of previous iPadOS albeit at a slower pace.