Back in iOS 12, the Screen Time passcode was stored in encrypted iPad backups. We have more on this on our blog post here deciphertools.com/blog/forgot-restrictions-passcode/ under "How to recover your iPhone or iPad Screen Time passcode (iOS 12)" Hope it helps!
These instructions should work for the iPad 6th generation also. If you don't see these settings options from the video, what version of iOS is on the iPad?
If you go into Settings > Your Name (the iCloud settings), is there a Family Sharing section? If yes, tap it. Are you listed as a parent/organizer, or a different account? If this iCloud account is on Family Sharing then one of the parent/organizer accounts can reset the passcode, as described starting around 48 seconds into this video.
What version of iOS is running on the iPhone/iPad that you're trying on? Do you have an idea of how long ago the screen time pin was set (not exact time, but "several years" vs "a few years"... so we can estimate how old of an iOS version set it?)
