There is the energy production, and there is the energy trading. It’s the traders who “deliver” the electricity to you, though in reality, it’s not since the actual grid doesn’t let the traders buy from a specific plant and deliver that specific power to your house.
So even if your energy company only buys power from green plants, like mine does, there is no guarantee that the power you actually consume wasn’t made by the fossil fuels plant next to you. It’s fine, but it’s also a little make belief.
Electricity production is not a monopoly and can work well as a market, but there needs to be oversight and rules for the trading.