bSupports2DTextureStorageMultisample is completely unused, while bSupports3DTextureStorageMultisample is practically unused. In the past, these were checked and fell back to sampler2DMS instead of sampler2DMSArray on GLES 3.1, but this path was removed in f039149198 and Dolphin always uses array textures now.
While the NV extension is totally fine, the KHR extension should be able to support more hardware.
For NVIDIA, the hardware either supports both or neither, it just needs a driver from the last two years.
For AMD, the drivers from late 2022-12 seems to bring support for the KHR extension.
For Intel, the KHR is also supported for some years.
Alfred Wingate