Best value lens for art documentation ?

[Zurbaran]

Hi.

I am condidering replacing my canon 6D+85mm f1.8 for documenting artwork (oil paintings)

I have a cross polarization setup using two Godox SL100D lights, and it works well, but I'm thinking of upgrading the camera for even better image quality and color fidelity.

The Fujifilm gfx 50R and 50s has started to approach manageable prices on the used market, but I am wondering about what lens to pair it with.

Autofocus is not a must, and I am only going to shoot the lens at its sharpness peak, say f5,6-8(?), so a fast lens is not necessarily needed.

I want very good corner to corner sharpness, and as little distortion or vignetting as possible naturally.

What would be the best choice on a budget?

I am considering using adapters of course, and I have been looking around for suitable older lenses such as the Minolta ROKKOR 85 f1.7 or 100 f2.5, but also Pentax 645 lenses.

I know very little about the available lenses however, so if you have a suggestion for me, it would be most welcome.