Ethereum has never reverted the blockchain which is what breaks immutability. In fact, you can go back in history and find the DAO creation, the hack, and even the transaction that reverted the stolen funds.

This is, by the way, unlike Bitcoin which did revert the blockchain and break its immutable nature in 2010. https://decrypt.co/39750/184-billion-bitcoin-anonymous-creat...

Not sure that this matters much but as it's a frequent point brought we might as well get the details rights.