Why The update 16 not shown on my iPad Pro 5th generation ???

iPad OS 16 will not be released until October.

Unlike iOS16 for iPhone, released yesterday, iPadOS16 is not due for release until sometime in October. 

However, iPadOS 15.7 was also released yesterday - incorporating essential security updates.

About the security content of iOS 15.7 and iPadOS 15.7 - Apple Support

While iOS16 is available for iPhone, iPhone owners have the option to just install iOS15.7 at this time.

iPadOS 16 coming sometime in October 2022.

Tap this link below.

iPadOS 16 Preview - Apple