Your iPad Air is likely working as intended…
Don’t be fooled by your iPad Air seemingly having four speaker grilles. Your iPad Air has only two speakers - not four as found in models of iPad Pro.
Recent models of iPad Air (i.e., iPad Air4 and Air5) have one speaker at top and bottom - such that what viewed in Landscape orientation, you will have a left/right stereo pair.
You can verify and compare iPad specifications here:
https://www.apple.com/ipad/compare/?modelList=ipad-pro-12-9-6th-gen,ipad-air-5th-gen,ipad-air-4th-gen
As a point of interest, older models of iPad Air had two speakers on the bottom edge of the iPad - one placed either side of the Lightning port. For these models, with the iPad positioned in Landscape orientation, both speakers where to one side of the screen.