Works with a plain adapter
Bronica ETR sits 49.75mm further from the sensor than Micro Four Thirds. You need a 49.75mm 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. The lens covers more than the sensor needs, so the body crops into the frame — roughly 2.5×. A 50mm frames like a 126mm would on Medium format.