Apps not compatible

The iPad 2, released by Apple thirteen years ago, cannot use an iOS version greater than 9.3.6. That version was current about eight years ago.

Application developers typically modernize their apps such that they can no longer support such an antiquated operating system.

As you have discovered, such old equipment is practically useless. Consider recycling it.

Each developer of an app makes the choice on what OS versions they want to continue to support. Most will concentrate their efforts on adopting new features from the latest updates. There is an advantage for them to continue to support older software as well to reach a wider audience, but for some it just does not make sense financially to spend their resources there on a market that continues to be smaller due to people upgrading their devices.