The problem with renewable resources is that most of them are pretty expensive which can take up to years to upset the cost. Just because fiat is the enemy of cryptocurrency doesn't mean that they are not innovating too, I think that there isn't going to be a need to cut trees anymore as time goes on because most fiat are slowly going to the polymer type of currency and most of the current fiat is not purely paper because if that were the case, a one time exposure to water is going to destroy that fiat, they are a mixture of cotton and other things to make it sturdy against elements.
It doesn't matter whether fiat currency is made of paper, polymer or cotton. All of these components are damaging to the nature, and the most important thing to note here is that the fiat banknotes needs to be replaced after a few years of usage. Polymer banknotes may last more compared to those made from paper, but even they have a limited lifespan. The beauty with Bitcoin is that once it is mined, the coins are indestructible.
And I agree with the argument related to renewable sources of energy. As of now, they are more expensive when compared to coal or natural gas generated electricity. But the gap is narrowing very rapidly, and very soon electricity from the renewable sources will be on par with that from non-renewable sources as far as the cost is concerned. In 2018, the average cost of solar generated electricity was estimated at $0.085 per KWh. Not as cheap as coal generated electricity, but not that high either.