This lock already exists and comes under the name Passphrase, and it is sometimes called hidden wallets, 13/25 word, or second password.

If you lose your seeds or someone knows them, you will be able to access your main account, which may contain zero dollars, but still needs a Passphrase to access your other account, which contains your main balance. You can create more than one Passphrase, and therefore for the same seed you can have more than one account, each account containing a different balance.
It is useful as a second layer of protection, but you need to keep it in a separate place, but it will not be useful if hackers gain access to admin privileges in your account, where they can record the screen or access the clipboard and copy Passphrase.