I have two more wallets that are encrypted and I know the password. I have used the command walletpassphrase "PASSWORD" 60 to unlock them for one minute and I immediately run the command dumpwallet. I was able to obtain the dump, but it does not contain any extended private masterkey. It's just a list of BTC addresses. Why is that so and how can I get the extended private masterkey for these wallet files?
How old are the wallets? Could it be that they are legacy wallets?
Legacy wallets are just collections of random key pairs and don't follow a descriptor-based derivation. So there is no master private key for these.