There has been a lot back-and-forth about Macro lenses adapted to Fujifilm GFX... Each option has a few strengths, as well drawbacks. I thought i listen them here:

TTArtisan 100/2.8 2x Macro
(Canon EF mount + adapter) or direct GFX mount

Let's get straight here:

• It is NOT a "native" GFX lens.
• It does NOT cover the larger GFX sensor.
• Performance at infinity is questionable, because of the strong blur in the extreme corners. Even the borders are a bit so-so, unless stopped down to ƒ11
• It vignettes at infinity
• It strongly vignettes at 2x macro

• It's strength lies between portrait distance and approx. 1.3 x macro, in which it shows no vignetting !
• It has adorable beautiful bokeh quality, even when stopped down. This shows off in the close-up and up to 1x macro range. It certainly has a kind of poetry without that "clinical" rendering, so to speak - but sharp in focus of the detail you wish to highlight.

• Using the TTArtisan 100/2.8 Macro as a scanning lens for film negatives with a Fujifilm GFX camera; extreme corners show that they never get truly sharp - not even at ƒ11 or ƒ16. Even the borders show an ever so slight blur (very little, but it is there). When used at ƒ6.7 this gets a bit worse at borders/corners)

• You can always spot a smear of the film grain, even at the borders/extreme corners at ƒ11, if you are really looking - you'll see it. Other parts of the image are sharp.

• The lens does not extend physically (IF, internal focus)

• I have not tested this lens with a extension tube. I assume corners sharpness gets worse, due to that i believe the lens exhibits floating lens elements. That usually makes corner sharpness worse

• Affordable price

Tamron SP 90/2.8 VC Macro (F017)
Canon EF-mount + EF-GFX adapter

• It vignettes at infinity and the wide open aperture sharpness is so-so.
• Vignetting diminishes as you focus closer down to 1x macro where it disappears entirely. I would say between 1:2 and 1:1 macro this lens' vignetting is insignificant. It is totally gone at / near 1:1

• Sharpness stopped down, focused from 1:2 to 1:1 macro - this lens shows evenly distributed sharpness from center to the extreme corners - even with a GFX camera; very good indeed! Making it great for scanning negatives.

• It appears to me, when looking at the second hand market, that many Tamron SP 90/2.8 VC Macro (F017) seem to stop auto focusing (often sold "as it is", with manual focus only). Maybe Tamron didn't get things right / not enough reliable on the model ? Nevertheless, as a macro lens, AF isn't of importance. I often use lenes in manual focus mode, when doing macro, anyway.

• The lens does not extend physically (IF, internal focus)
• Affordable, but questionable second hand price / not many left on the market.

Sigma 70mm ƒ2.8 ART Macro
(Canon EF-mount) + EF-GFX adapter

• A very sharp lens at all distances !
• Bitingly sharp.
• Does not really vignette at infinity !
• Vignettes between 1:2 and 1:1 Macro
• Works wonderful as a manual close-up on GFX, but vignettes when going really close.
• Perhaps (in my opinion) among the very best Macro lenses for fullframe cameras.
• As a scanning film lens on GFX, it does it vignette in the extreme corners which can be annoying to correct.
• Extreme corerns however, remain sharp !

• Not recommended with extension tubes, due to that it exhibits floating lens elements, which screw up corner sharpness (but corner shading disappears).

• The lens extends when focusing
• This is my Macro lens to go, when scanning 35mm negatives - best quality you can get.
• Affordable price !

Olympus m.Zuiko ED 60/2.8 Macro (50-80 MP Pixelshift mode)
(for certain MicroFourThirds cameras only)

• Sharp and highly flexible lens, good at all distances in normal photography & macro (without pixelshift)

• When used with Olympus / OM System's 50 to 80 MP pixelshift - you do get good images overall indeed, when looking at a photo as such - But i call this Pixerltechnology highly in question; as it doesn't truly show muhc or if any at all extra resolution. Especially when you compare that to a native image sensor of 50 MP. I find the scanned negatives to have slightly less finer details, kind of mushy, which gets weird when sharpening. But it is an option - and the final output looks sharp, even and there are no dark corners to speak of.

• Pixelshift 120-film film scanning works very well, when used with ISO 400 films and color negtives in particularly.
• Lens is sharp from center to corner
• Doesn't exhibit corner shading

• IF, internal focus - the lens does not extend when focusing

Fujifilm GF 120 mm ƒ4 R LM OIS WR Macro
Native GFX lens

• I have no practical experience from this native GFX Macro lens and therefore remains theoretical:

• The lens if of course very sharp. At 1:2 (half macro) the borders are slightly less sharp.
• Exhibits very evenly distributed sharpness when uses as a normal lens (infinity) and in the portrait range
• The lens only goes down to HALF macro, not full macro

• When an extension tube is used in order to obtain 1:1 Macro, the optical performance deteriorates significantly at the borders and extreme corners - which has been highly criticized my many serious macro photographers, how bad this lens performs with tubes ! (The floating lens element is what stands in conflict with extension tubes; leading to worse performance / worse corner sharpness due to that the plane of sharpness bends towards the corners / aka the field curvature increases) making it no good for flat objects (such as negatives)

• The high price point of at least 2900 € / 29000 SEK and mediocre "1:1 macro" performance when tubes are used, makes this lens' value a bad choice / highly questionable choice if Macro with a Fujifilm GFX camera is your primary goal.

• IF / Internal focus, the lens does not extend when focusing

Pentax 645 SMC FA or A 120 mm ƒ4 Macro lens +
P645 to GFX adapter

• I have no practical experience from this native GFX Macro lens and therefore remains theoretical:

• This lens focuses natively down to 1:1.
• It is regarded to be the best / more affordable ones among manual 645 mediumformat Macro lenses.
• Does not vignette
• manual focus only with GFX (of course)
• Evenly distributed sharpness when stopped down
• Does extend when focusing.

Other options ?
6x6 and 6x7 film negativ scanning with Fujifilm GFX cameras

I have not experimented other options or lenses any further. Such as reverting a lens by mounting the front via an adapter to the camera body, in order to get good macro performance / sharpness. Or using enlarging lenses or industrial lenses via a bellow. Not have i tested it with other vintage macro lenses such as Canon FD 50/3.5 1:2 macro (half macro), etc.

• I read that when using more modern Canon EF Macro lenses on GFX, they do exhibit corner vignetting, both Canon EF 100/2.8 Macro and Canon EF 100/2.8 L IS Macro.

Supposedly an old Canon Macro FDn 100/4 Macro (half macro 1:2) does not vignette. And it shouldn't with an extension tube either, because it does not have floating lens elements. (The lens costs 100€, looking good actually). But I haven't read anything about the sharpness performance on the GFX sensor and the corner sharpness in question.