How can I update my iPad stuck on iPadOS 16.3.1?

I purchased a 9th generation iPad from a family member and reset it to factory settings. It is now stuck on IOS 16.3.1 and will not complete the installation of version 18.6. My iPad should install the software with not problem. I have plenty of storage, but I can’t find a way to bridge the gap in the operating system.

Can you help?

[Re-Titled by Moderator]

Original Title: Help Updating IOS on iPad