ipad

You can directly compare major features of the various models of iPad here:

iPad - Compare Models - Apple

In summary, the iPad9 is the entry-level iPad. At the other end of the scale, the iPad Pro models represent the pinnacle of performance and features - with a price to match. The iPad Air is a high performance mid-point, offering much of the “performance” of the iPad Pro - but lacks the advanced hardware features of the Pro models (such as orientation adaptive multi-speaker audio, advanced camera array, LiDAR sensor etc.).

The current iPad Pro 12.9” also features the newest XDR miniLED display - this being exclusive to this model.

You can compare the 2 devices by clicking on iPad in the black stripe at the top of this and every forum page. This will take you to the online store where you can compare items easily.