I've just been comparing the iPad Air 3 with the iPad Mini 5th gen (1st & 2nd prizes in the just run AUSOM annual raffle) and the differences are minimal, restricted to physical size & the Air having a Smart connector for attaching a keyboard.
As for screen resolution, the Mini's effective resolution (due to a smaller screen) is 326 ppi vs the Air at 264 ppi. Internally, other than a larger battery (both offer the same battery life in theory) they are identical in specification.
Both are available in 64 GB & 256 GB configurations. Both have the A12 Bionic processor and M12 co-processor with 3 GB of RAM & 6-core processors.
So thie iPad Mini I won a few days ago in a raffle is a shrunken version of the iPad Air 3.