The battery health feature has, until very recently, been exclusive to iOS for iPhone.
Prior to release of the 2024 iPad Pro M4 and iPad Air M2 models, iOS/iPadOS for iPad has never had the Battery Health feature. The iPad Battery Health feature remains, at this time, exclusive to these new models:
About iPad battery health and history on iPad Pro (M4) models and iPad Air (M2) models - Apple Support
As such, this feature is not available for your iPad9.
Be aware that all iPad batteries are rated to maintain at least 80% of their initial capacity after 1000 full charge/discharge cycles - whereas most models of iPhone are rated to have 80% of initial capacity after 500 full cycles. There are software packages available that can access battery cycle count. Popular choices for Mac are Coconut Battery and iMazing - whereas iMazing is available for PC.
https://www.coconut-flavour.com/coconutbattery/
There are additional methods to estimate the Battery Health of an iPad - these being reliant upon third-party Shortcuts that can extract data from iPad Analytics files. If this interests you, search for "Battery Health" within the Shortcuts App Library.
If you are experiencing difficulties with your iPad battery holding charge, you might be best advised to first have your iPad tested.
If you directly contact Apple Support - and explain your problem - you can request a remote battery diagnostic. The tests will confirm the status of your battery - and other elements of your iPad’s health.
Alternatively, a visit to the Genius Bar at your local Apple Store would provide opportunity for your iPad to be similarly tested by the Apple technicians - after which you can explore your available options.
You can contact Apple Support using the Contact Support link at top-right of this page. You can also initiate a support case using the excellent Apple Support App; if not already installed on your iPad, the App can be downloaded from the App Store:
https://apps.apple.com/gb/app/apple-support/id1130498044