I don't know much about grapes, I have only seen the vineyards, but I think that if you take it out to a bigger container and put it in a place where the branches can support, the grape plants can grow a lot, I have a friend who has a small vineyard in his apartment.
So I recommend that, take it to a place where it has more space and I bet you will have a good harvest all year round.

Consult with someone who knows, because from that plant you can get some cuttings to have more plants, that is a genetically equal copy of the mother plant, so you would have many more grapes.