Why I am not able to check coverage of my mouse and keyboard?

Keyboards and Mice are not tracked by Apple’s warranty support site. Never have been. They are covered by the warranty of the device purchased.

https://store.apple.com/Catalog/US/Images/AppleCareProtPlanFacts.pdf

1. Assistance with the complete
2. Apple solution
3. Apple hardware products3

• • – An Apple computer
• – An Apple mouse and keyboard when
• included with a covered computer (or
  • purchased with Mac mini)

What do you mean by that? Are you talking abut warranty coverage? Please be more specific about what you are asking.