Battery endurance between charges will be affected by many factors - such as the App(s) used, CPU/GPU load, screen brightness and temperature. Some graphics intensive Apps are particularly power-hungry - although four hours use before requiring recharge does appear rather low.
If both you and others are experiencing the same issue, assuming that you are using the same Apps, this might suggest that the App (or Apps) themselves are the issue.
If you continue to experience difficulties, you might be best advised to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page.
Alternatively and perhaps easier, you can initiate and manage your support cases 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
You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad and Pencil:
Genius Bar Reservation and Apple Support Options - Apple