gandlaf21 on Nostr: this depends on the attack, But if the attacker knows the seed phrase, the passphrase ...

this depends on the attack,

But if the attacker knows the seed phrase, the passphrase needs to have ~70bits of entropy.

Per truly random alphanumeric character, you get about 6bit per character. so you need 12 minimum

If the passphrase is not truly random, the bits you get per character sink drastically (eg. it includes well known sequences or numbers)