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