You are not going to want to read this, but here it is, anyways.
At this late time, your iPad 3rd generation is an over 8 year old device now.
There is no trade-in value for any 8, 9 or 10-year old iPads.
Support from Apple for these old iPad models ended 4 years ago.
Virtually all third party app support for these old iPads completely ended over 2 years ago.
These 8 and 9 year old iPads are completely and fully unsupported now with NO upgraded/updates to ever be forthcoming.
Sorry.
If you need/want the more advanced features of the latest iPadOS, then you need to seriously consider the purchase of a new or much “newer”, used iPad model that is capable of running the latest iPadOS versions.
There a plenty of newer, older models of iPad that can run the latest iPadOS.
Best of Luck to You!