I’m a bit confused about the claim that the image was altered.

Sometimes skies look like that and grass looks like that and (the right) film is more than capable of capturing that with the appropriate saturation. Especially Velvia. Velvia is probably even cranking up the saturation, to levels you would not see like that with the naked eye.

Here is a landscape photographer showing their own favorite Velvia photographs: https://www.macfilos.com/2022/12/02/vivid-velvia-ten-fujifil...

Look at that first Tuscany image. The colors are a near perfect match. With the others the colors - especially the greens – can also be a lot more muted, however that seems to be down to darker greens as a starting point and also the light/weather (less saturation when it’s overcast and there is no direct light).

On close examination of the wallpaper (to a level of detail not visible on early 2000s screens) also shows all the hallmarks of a real photograph with remarkably little retouching.

On the left and especially the right you can see ugly clutter behind the hills which is only not distracting if you don’t examine the photo to closely. Anyone who photographs landscapes knows the issue of hard to hide clutter that nevertheless from my perspective also grounds the photograph in the real world.

Also clearly visible on the hills: tracks/paths through the hills. This is also something hard to avoid in landscape photography, though you try to minimize it with perspective. The same applies as to the clutter: my view is that this grounds the photograph as an actual photo.

Third hallmark of photography: the foreground grass is all out of focus! This is often hard to avoid. Techniques like focus stacking now exist, but as a single photograph that is often a trade off you have to make if your landscape shows both things close by and far away.

So, yeah, looks 100% like a real photograph and shows what a look Velvia is, mostly.