Ethereum [sic] is moving to PoS from PoW, but ETH doesn't suffer the same growth issue that BTC does because its hash algo is effectively tied to its hardware. It can run on PoW indefinitely and will likely do so for several more years until PoS is fully ready.
There are a few asic's for ETH, but the hash algo is fundamentally executed through memory. Even if you build an asic for ETH, you are always tied to the speed of memory.
Therefore, a GPU is going to be the most ROI efficient mechanism for a long time (asics cost more to build than a commodity GPU) and even more so, older GPUs work just as well from a ROI perspective because newer GPUs are more expensive.
This means ETH does not see the same hashrate growth (and energy usage) as BTC, while maintaining the same level of security.
The vast majority of energy usage for blockchains, is green energy hydropower using excess power from facilities that already exist. Why? Because this is the lowest cost and prior to this current bull run, was the only way to be profitable.