That's true, and as far as my quick research has gone, the plastic is burned off during the smelting process of aluminum recycling.

Because of the small amount of plastic in each can, and the high heat of the smelting process, odds are good the thin plastic liner will be almost fully combusted, which should greatly reduce the amount of microplastics.[1]

1: https://www.sciencedirect.com/science/article/abs/pii/S03043...