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.
must always try to keep backward compatibility.
It will, as the key generation scheme used by Electrum differs from bare BIP39
https://electrum.readthedocs.io/en/latest/seedphrase.html Right now client is in position to import BIP 39 SEED but says it can not guarantee that option in the future. You can check it.