It is. Always has been.

The seed without the passphrase leads to a wallet (call it Wallet A). Adding the passphrase to the (same) seed leads to another wallet (call it Wallet B). Wallets A and B are cryptographically independent, and there is no way to get to one from the other. Any other passphrase you add to the (same) seed leads to Wallet C, D, E, etc.

So, Wallet A can be empty (or have a small amount, say, 1 BTC, as a decoy, for $5 wrench attacks), and at the same time Wallet B can have the bulk of your stash (say, 100 BTC). This setup can be used for plausible deniability (you disclose the seed, but not the passphrase).

All this is part of BIP-39, and is compatible with all BIP-39 wallets (Trezor, Ledger, etc.).