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Whether a specific lens with an apodization filter has very much light falloff in the corners and at the edges is pretty much the same as it is for any other lens - it all depends on the design of the lens. The apodizing filter will add some vignetting, but 100mm lenses don't typically have much light falloff (compared to wide aperture wide angle lenses) to begin with.

What will change is that the total light transmission of the lens will be less. Even though the entrance pupil size wide open is f/2.8, the neutral density of the apodization filter gives it a transmission of only T5.6. The aperture settings on the lens are marked in T-stops, rather than f-stops.

Whether a specific lens with an apodization filter has very much light falloff in the corners and at the edges is pretty much the same as it is for any other lens - it all depends on the design of the lens. The apodizing filter will add some vignetting (compared to another otherwise similar lens of the same focal length using an f-number that is equal to the apodizing lens' T-stop number - because some of the light outside of, say, the diameter of an f/5.6 entrance pupil is being allowed through by a T5.6 setting on an apodizing lens), but 100mm lenses don't typically have much light falloff (compared to wide aperture wide angle lenses) to begin with.

What will change is that the total light transmission of the lens will be less. Even though the (partially blocked) entrance pupil size wide open is f/2.8, the neutral density of the apodization filter gives it a transmission of only T5.6. The aperture settings on the lens are marked in T-stops, rather than f-stops.

At T5.6 the Sony FE 100mm F2.8 STF GM OSS will provide the shallower depth of field of a more traditional lens set at f/2.8 while only giving the light transmission of a traditional lens set at f/5-5.6. The whole point of the apodization filter is to eliminate bright edges in the bokeh of out of focus highlights. But in landscape photography the goal is typically to not have anything out of focus to begin with.

At T5.6 the Sony FE 100mm F2.8 STF GM OSS will provide the blurry out-of-focus areas of a more traditional lens set at f/2.8 while only giving the light transmission of a traditional lens set at f/5-5.6. The whole point of the apodization filter is to eliminate bright edges and irregular shapes in the bokeh of out of focus highlights. But in landscape photography the goal is typically to not have anything out of focus to begin with.

So the real question is more along the lines of why would one consider such a lens for landscape work where greater depth of field is usually desired, bright edges of out of focus highlights are not usually a concern, and image stabilization is irrelevant when shooting from a tripod? At T5.6 the Sony FE 100mm F2.8 STF GM OSS will provide the shallower depth of field of a more traditional lens set at f/2.8 while only giving the light transmission of a traditional lens set at f/5-5.6. The whole point of the apodization filter is to eliminate bright edges in the bokeh of out of focus highlights. But in landscape photography the goal is typically to not have anything out of focus to begin with.

On the other side of the equation, you will see slightly more vignetting with the Sony 100mm than with other more traditional lenses at narrower apertures. The other lenses in the comparison above show very little vignetting at f/5.6 and beyond. The Sony 100mm maintains the same amount of vignetting all the way to T22.

You'll also get more vignetting at apertures of f/5.6 and narrower than with a typical 100mm f/2.8 lens without the apodization filter.

So a very real question could be more along the lines of why would one consider such a lens for landscape work where greater depth of field is usually desired, bright edges of out of focus highlights are not usually a concern, and image stabilization is irrelevant when shooting from a tripod?

At T5.6 the Sony FE 100mm F2.8 STF GM OSS will provide the shallower depth of field of a more traditional lens set at f/2.8 while only giving the light transmission of a traditional lens set at f/5-5.6. The whole point of the apodization filter is to eliminate bright edges in the bokeh of out of focus highlights. But in landscape photography the goal is typically to not have anything out of focus to begin with.

The acutance of the Sony FE 100mm F2.8 STF GM OSS is impressive, even when compared against a lens such as the Carl Zeiss Makro-Planar T 100mm f/2 ZE.

On the other side of the equation:

• You will see slightly more vignetting with the Sony 100mm than with other more traditional lenses at narrower apertures. The other lenses in the comparison above show very little vignetting at f/5.6 and beyond. The Sony 100mm maintains the same amount of vignetting all the way to T22.
• You will also see pincushion distortion not typical for a 100mm prime lens. (see below)
• You will also see more chromatic aberration, particularly in the mid-frame areas, than other more conventional 100mm prime lenses. (see below)

Again, you'll get more vignetting at apertures of f/5.6 and narrower than with a typical 100mm f/2.8 lens without the apodization filter.