https://arstechnica.com/gadgets/2022/06/ipados-16-waves-goodbye-to-the-ipad-air-2-but-supports-most-older-hardware/

According to Apple's press release, iPadOS 16 will run on the following models:

That means that 2014's iPad Air 2 (which Apple sold for years as a lower-cost model, before the $329 iPad came along) and 2015's iPad mini 4 won't support the new OS but that most other models that can upgrade to iPadOS 15 will also be able to run iPadOS 16. Apple may continue to provide iOS and iPadOS 15 security updates for devices that can't upgrade to iPadOS 16, but we'll need to wait for confirmation before we know that for sure.