Works with a plain adapter
Four Thirds sits 11.97mm further from the sensor than Fujifilm G. You need a 11.97mm adapter, but it can be a plain one — a hollow metal spacer with no glass in it. The lens still reaches infinity focus and nothing is added to the optical path.
Coverage & framing. Four Thirds lenses are built for a Micro Four Thirds imaging circle, which is smaller than Medium format. Expect heavy vignetting or a forced crop on a Fujifilm G body.