Unfortunately, there is no safe way to store this material. If you put it in the landfills, it leaches out as microplastics. If you incinerate it, you get chemicals into the air, and some microplastics if it's not done correctly. There's no safe way to do this.
For the moment, until we find something, we should be landfilling, but that's a temporary fix. We should be sorting the plastic we put in the landfills so that we can recover it easily and we know we have that type of plastic stored here. We can go back and get it later when we can do something safe with it.
We can't let the industry decide what that word means. The plastics treaty, for example, is something that scientists need to be paying attention to a bit more.