This is not Apple's doing, but the fault of third party app developers.
If your iPad was waaay behind in iOS/iPadOS upgrades/updates, older apps that were older 32-bit apps that have been long unsupported and no longer upgraded to Apple's newest 64-bit code way back in 2016/2017 with the introduction of iOS 11, will NO longer launch or function.
It's 2021 now.
It is highly likely these apps will never be upgraded, at all, at this late date.
These apps, also, may no longer even exist in the iOS App Store, any longer, either.
This is NOT the fault of Apple.
The Apple iOS App Store is a marketplace for third party app developers where Apple takes a monetary percentage of the price the third party app developer puts on an app. App developers are selling the rights to the use of their apps to users.
You only, basically “rent” software on iOS devices.
Third party app developers can, and DO, for a myriad of reasons, stop supporting their software on iOS/devices at anytime without warning to its users.
There is nothing to be done.
Sorry.