I haven’t tried the Quest 3 in MSFS, but used to use the Oculus Debug tool and messed around with the supersampling figure to achieve the native resolution displayed in the MSFS graphics options (It involved a lot of decimal points to get 2736 for the Quest 2).
Now I believe the best option for the Quest 3 is to buy Virtual Desktop which now has native support for OpenXR. You can change supersample to the desired resolution easier and get performance improvements. Virtual Desktop "native" OpenXR support is here!