Use a Passphrase

Instead of simple numeric passcodes or complex random strings mixed with special characters, use a passphrase as your “Custom Alphanumeric” passcode.

https://www.useapassphrase.com/

You will have to type this password once in a while and this can be a bit annoying, but 99% of the time you’ll get by with biometrics so it’s not as bad as it seems.

Set an Alphanumeric Code as iPhone Lock Screen Passcode

This is an important passcode and it should be stored in your Password Manager.