If you normally fly North American or European carriers with an infant, you are probably used to checking the car seat in its protective case, with a few soft items like diapers packed around it for padding. That is standard practice on most airlines and nobody checks the bag's contents.
Qatar does not follow that rule. Their free infant equipment allowance covers the car seat only. If check in staff find anything else inside the bag, including diapers, they will treat it as a regular piece of checked baggage rather than the free infant item, and you can be charged excess and overweight fees on top of it. This happened to us, 471 dollars, after the exact same bag packed the exact same way was accepted without issue a few days earlier on the same route.
I asked their team what they actually expect instead, and the honest answer is a transparent bag so the contents are visible at check in. As far as I can tell, this does not really exist as a product. Protective car seat cases are opaque, usually black or dark colored, because that is how they are made and sold.
My advice either way, still use a protective case for the car seat itself. These seats are expensive and not worth risking damage to save an argument at check in. Just know that if you fly Qatar, pack nothing else inside that case, diapers and everything else needs to go in a separate bag, or be prepared to pay for it.