Begin by restoring to Factory Settings - as this will fully erase the iPad and clear any lingering issues:
Restore your iPhone, iPad or iPod to factory settings – Apple Support
Next you can restore your pre-existing backup
Restore your iPhone, iPad or iPod touch from a backup – Apple Support
Restore all content to iPad from a backup - Apple Support
You’ll need access to either a Windows PC (with iTunes for Windows installed - or for Windows 10/11, you will need the more recent Apple Devices App) or a Mac computer (with iTunes or Finder - as appropriate for the installed version of macOS).
Download and use iTunes for Windows – Apple Support
Update to the latest version of iTunes – Apple Support
Apple Devices App (Windows PC):
https://apps.microsoft.com/detail/9np83lwlpz9k?hl=en-ms&gl=MS
Use of a PC or Mac computer is unavoidable. If you don’t have access to a suitable computer of your own, that of a helpful friend or family member will suffice. Alternatively, the technicians at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP) will be delighted to assist.
Genius Bar Reservation and Apple Support Options - Apple