Don't get me wrong, I think electrum wallet itself is brilliant but there are now better alternatives like Trezor which do adhere to the BIP39 standard and reduce confusion in the community. Electrum is making it harder to recommend them because they are non-standard.
Electrum wallet itself is also compatible with BIP39 seeds... so while you can't
generate a BIP39 seed within Electrum, you can still
use a BIP39 seed (generated elsewhere) with Electrum to restore a wallet.