Well, Porygon is a digital pokemon, isn’t it? If I’m remebering right, it’s made of code. So Porygons would likely be more widely available near silicon Valley-like metropolitan areas than any natural biome. To be an invasive species, it would need to be available in those places and out compete native pokemon for resources, and I don’t see how an artificial pokemon made of code could do that in most biome, it’d be a non-native or introduced species at most.