They were accepting donations in Bitcoin for years.
No way back from there

Looks like they are trying anyway.
https://www.coindesk.com/markets/2021/05/21/greenpeace-stops-accepting-bitcoin-donations-cites-high-energy-use/Environmental campaign group Greenpeace USA has stopped accepting bitcoin donations over the carbon footprint of the cryptocurrency.
According to a report from the Financial Times on Thursday, the organization said:
"As the amount of energy needed to run bitcoin became clearer, this policy became no longer tenable."
At some point everyone realized that it is PoW or them, and they they refuse to use it.
Everyone except bitcoin cultist that are utterly delusional about Proof of Waste. Greenpeace realize that PoW was a danger in May of 2021,
Texas will realize the PoW danger, when their power grid collapse in 2024.