OK. bare BIP39 is still supported but likely be deprecated in the future versions, at least that is what 3.3.8 client says right now. Anyway the generation scheme of the current and all future Electrum is different from bare BIP39.
https://electrum.readthedocs.io/en/latest/seedphrase.html That is why you had to scroll down to find that address.
i haven't seen the "deprecated in the future versions" anywhere, and i don't think features like that would ever be deprecated because wallets must always try to keep backward compatibility.
in any case if some day some wallet stopped supporting BIP-39 you can always find another tool (like IanColeman tool) and convert the mnemonic to an extended private key (starts with xprv) to use the more universal master key to import. or worst case scenario import individual keys.