I had the Zeiss ZE 2.8/21mm, ZE 2/35mm, ZE 1.4/50mm and ZE 1.4/85mm adapted to the GFX50R with the Kipon EF>GFX AF. I sold them all.
2.8/21mm: horrible hard vignetting with no chance of recovery except with a big crop in the image and distortions.
2/35mm: vignetting and chromatic aberrations.
1.4/50mm: very bad between f1.4 and f2.8; lack of contrast and sharpness. Vignetting and chromatic aberrations.
1.4/85mm: very bad between f1.4 and f2.8; lack of contrast and sharpness. Softest vignetting of the four and chromatic aberrations. At f1.4 there was a very strange effect that looked like an "Emboss".
It's no coincidence that the 1.4/50 and 1.4/85 were completely redesigned when they became Milvus. They are beautiful objects but optically weak. Why have f1.4 if you can't use it? Apart from vignetting, these problems were present when I used them on the Canon 5DII/III/IV and EOS R cameras.
I now only have the ZE 2/100mm Macro-Planar. It does a bit of vignetting (recoverable) and optically it's superior to all the others I've mentioned. The Zeiss APO Sonnar T* 2/135mm ZE/ZF2 is very good too.
This table isn't always accurate, but it has its uses.
I'm curious to know how the Carl Zeiss Planar 2/50mm T* ZM - Leica M Fit behaves in the GFX with respect to vignette. I hope it's better than the ones I had

If anyone has already tested it, I'd be grateful if you could share your opinions and, if possible, images. Thanks.