Does a fruit battery work when the metals are the same?

No it does not.

Batteries work by electrons wanting to go from one terminal of the battery to the other, from the cathode to the anode. And for that to happen the metals have to be diffferent.

As a crude comparison: think of the metals at the terminals as buckets of water, interconnected by a hose by the bottom. With the same metal, both buckets are at the same height, and no water will flow between them. With different metals, one bucket can be lower or higher, making the water(the electrons) flow from the higher to the lower bucket.