Upgrading/updating that iPad any farther will never, ever be possible.
If your iPad model has been stuck on iOS 9 or 10 for all of these past years, then it is possible you own an over 9-1/2 to 10-1/2-year old, 2011 iPad 2 or 2012 iPad 3, 4 or 1st gen iPad Mini.
These iPad models cannot ever upgrade beyond iOS 9.3.5/9.3.6 or 10.3.3/10.3.4.
An over 9-1/2 to 10-1/2-year old iPad is far too old, now.
Sorry.
Apple ended support for all 8-10-year old iOS devices nearly 5 years, ago, in 2016.
Third party app developers abandoned and stopped supporting these 8-10-year old iOS devices nearly 3 years, ago, in 2018.
There are, virtually, NO MORE third party apps available from the iOS App Store, any longer!
Third party compatible apps for such old devices are few and far between, now, at the end of 2021.
This includes apps for both iOS 9 AND iOS 10 devices!
AND, NO WAY to, initially, install any older, compatible, third party apps into this old iPad, any longer!
NO MORE SUPPORT! NO MORE APPS!
All 2011-2012 iPad 2, 3, 4 and 1st gen iPad Mini models are fully and completely unsupported AND obsolete!
Sorry, but this is the reality for ALL 8-10-year old AND OLDER iOS devices now. Especially now, at the end of 2021!
In addition, the internal, rechargeable batteries in these old iPads are, also, running on borrowed time.
Not worth the costs to replace these old internal, rechargeable batteries in these old iPads, any longer, either.
You really need to seriously consider a purchase of a new iPad model OR a much, MUCH “newer” and less expensive, refurbished or used iPad models, from better known, trusted Apple product/device retailers/resellers, some locally or from online, on the Web/Internet, capable of running the latest iPadOS versions.
There are PLENTY of less expensive, newer, older iPad models that can run the latest, current versions of iPadOS.
If you need OR ONLY able to purchase older, less expensive iPad models, look at older IPads from 2014 and later.
All of these older model iPads below, CAN run the latest releases of iPadOS 15.
2014, 9,7 inch screen iPad Air 2 models ( NO Pencil support )
2015, 7.9 inch screen iPad Mini 4 models ( NO Pencil support )
2015-2017, 12.9 inch screen iPad Pro models. ( 1st gen Pencil support )
2016, 9.7 inch screen iPad Pro models ( 1st gen Pencil support )
2017,10.5 inch screen iPad iPad Pro models ( 1st gen Pencil support )
2017, 9.7 inch screen iPad 5th gen models ( NO Pencil support )
2018, 9.7 inch screen iPad 6th gen models ( 1st gen Pencil support )
2019, 10.2 inch screen iPad 7th gen models ( 1st gen Pencil support )
2020, 10.2 inch screen iPad 8th gen models. ( 1st gen Pencil support )
2019, 7.9 inch screen iPad Mini 5th gen models ( 1st gen Pencil support )
Get the largest internal data storage model you can afford as NO Apple iOS device has ANY expandable storage.
I am sorry that you had to learn all of this, but this does not change any of the facts regarding these very old iOS devices.
Sorry & Best of Luck to You!