It is a common misconception that an iPad (or iPhone) can remain fully functional with damaged or defective physical buttons. Whilst Accessibility features (such as assistive touch) can be used to augment the User Interface, these features cannot be used as a substitute for physical button sequences that must be used to trigger system recovery actions. Sooner or later, you may encounter a situation from which you cannot recover.
Until repaired, you will not be able to resolve a locked-out (disabled) iPad - or reset a forgotten device passcode.
You would be well advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively 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/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 hands-on test and assess your iPad. If a fault is identified, you'll be in the best possible place to explore your available options:
Genius Bar Reservation and Apple Support Options - Apple
Apple also offer a mail-in repair service:
https://support.apple.com/ipad/repair