Single core performance is faster on Air 4, but multi-core definitely goes to Pro. More RAM for the Pro too.
ProMotion is a superior feature of the Pro, as well as quad speakers.
The Air has TouchID if you prefer it over FaceID. Also, the Air has more color choices.
For the same price, I’d probably go with the Pro. I chose the Air 4 over the 2020 Pro, and even though it works fine, there are minor shortcomings in the display and speakers, which are very important parts of the iPad experience for me.
The Air is a solid iPad, but it’s a compromise. It’s not the best of the best, while the Pro is the top-of-the-line. I do realize the 2021 Pro is truly the best, but the 2020 Pro is no slouch.