I'm cautious about being my own echo-chamber, but it's hard to resist when an article perfectly encapsulates your own point of view.
This article by George Monbiot in today's Guardian is perfect, and important; and opens the door to further thought (though not much further) about the power to change things. Anything. Read it, please, but the main thrust of the argument is that individual change (so far as one can, in the wider context) is trivial within that context:
As he says, "The problem is not just plastic: it is mass disposability." Any change exists within its own ecosystem and generates effects throughout that system. The change that is required is not that supermarkets be granted the additional income stream of mandatory charging for plastic bags - bags that require tens to hundreds of uses to offset the impact of single-use plastic - but that the economic ecosystem that demands growth at the expense of all else be changed. How does that happen?
The automatic response to that question is government, policy and law. But single countries exist within their own political ecosystems. A tax change in one country causes the corporations to relocate to a more favourable setting. A global treaty in this respect is fanciful at best and risible at worst. Individual companies exist within the ecosystem of their industry marketplace, and one company obtaining its raw materials from anywhere other than the cheapest source will be beaten and eaten by its less ethically-conscious so more profitable and powerful competitors. Likewise sole traders.
This is a species-level issue, and while individual people or semi-mobilised groups clicking online petitions might chip away comfortingly at their own personal impacts, it will have no effect on the trajectory of the top-level zero-sum ecosystem of our planet.
Read Monbiot though. He's more positive than me.