It is more about the complexity of algorithm security. RSA encryption is 2048bit, 8 times more secure than SHA-256. Quantum computers do have the ability to calculate something like a seed phrase. This is a trade off because only the government would have the ability to crack your wallet, But it can be done. There are brute force programs on GitHub, Where people have cracked wallets as well. Someone would need to make you specifically a target, And invest time and energy, But cracking a wallet is possible. Check out Sagemath language.