Immutable so long as no one party or group owns more than half of the coins on a given blockchain… then the ledger is whatever they say it is and it propagates down because they can manufacture their own “consensus”.

https://www.investopedia.com/terms/1/51-attack.asp

and most use cases around things like “smart contracts” end up still requiring a trusted third party at some point

https://pluralistic.net/2022/01/30/the-inevitability-of-trusted-third-parties/