I'm confused by your logic and reasoning here... You can totally using existing seed phrases/master public keys to create a MultiSig wallet. Yes, it will generate different keys/addresses, but you can still create a MultiSig address using them.
I experimented it immediately went I saw the OP question before posting.
I used two old Electrum standard wallet seed phrases and both generated
Zpub keys while importing it on multisig, that is entirely different from
zpub keys that they both are on standard wallets. And this can be used to set up the multisig wallet that its keys will be surely different, but which I advice better to generate new seed phrase instead.
I used the
zpub keys from the standard wallet but it displayed this error 'Wrong key type p2wpkh'.
What do you mean by a "single pubkey" wallet? Huh Do you mean a wallet that has been imported using WIF keys? Huh Because they don't even have master public keys... and Electrum doesn't even support creating single address MultiSigs... it has to be done using seed phrases or master keys.
All I was referring to are zpub key and Zpub key.
I think maybe he is confused due to the different types of public key between different types of Electrum wallet.
I was not confused about the master public keys in relation to what HCP posted, although I did not know one started from upper case and the other as lower case, but I did understand what happened and that the zpub dispalyed error while importing it as multisig type. Thanks for pointing that out.