Missing extended private masterkey

I've got a few old wallet.dat files sitting on my computer that are probably empty. Just to play it safe, I'm looking for a way to check their balances without needing to re-sync the whole blockchain repeatedly. I managed to use the dumpwallet command to get the extended private masterkey from one non-encrypted wallet and imported it into Electrum. It worked well. But now I've got two more encrypted wallets that I know the password for. I used the command walletpassphrase "PASSWORD" 60 to unlock them for a minute, then ran dumpwallet right after. I got the dump, but it doesn’t include the extended private masterkey. All I've got is a list of BTC addresses. What’s going on with that, and how do I get the extended private masterkey from 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.

They might definitely be legacy wallets. I think I created them back in 2013 or close to that. So that means that there is no easy way to import them into Electrum? My only option is to sync the entire blockchain (which is taking forever)?

Create a new wallet, choose "Import Bitcoin addresses or private keys", and import the addresses. You'll create a watch-only wallet that shows your balance. Note and disclaimer: if you happen to have mined or received "to pubkey", it will NOT show up this way!

OP, be careful with PM (Personal Message) that claim they can help you since usually it's scam attempt. Looking at https://bitcoincore.org/en/2016/08/23/release-0.13.0/, HD wallet support exist since 2016. Also note that if there are too many TX with those address, Electrum may take some time to get all data, feels laggy misbehave.