I would rule out the Air 3 on the basis that it and the 9th Gen have the same 3GB RAM. The 9th Gen also has the better chip.
The 10.5 Pro has an extra GB of RAM, the same as the Air 4, so there are benefits to that, especially with Procreate I’d have thought. The A10X was said to be somewhere in line with the Air 3’s A12 at release, so if you wanted the extra 0.3 inch of screen I would go for that, as the Air 3 doesn’t seem to have resolved the white spot issue as was thought and hoped on release. May as well get the quad speakers and promotion if you are taking the chance.
It mainly comes down to whether you are more concerned with the better chip (in which case get the 9th Gen) or RAM (get the Pro.) If you can stretch to a refurb Air 4 then you wouldn’t have either trade off and it avoids the white spot - you just wouldn’t have the quad speakers and promotion as they are yet to make it to the Air line.