Seed for bitcoin-core qt
You can export private keys from Electrum and BitcoinCore. You can export private keys from Electrum as "words" format (There's a website to convert it to private key(s): https://iancoleman.github.io/bip39/), while Core doesn't have this feature. See the steps in question Using dumpprivkey to make a paper backup to use dumpprivkey in Core to export the private key.