Four-button, expandable, PIN code lock mechanism, built on a flat creative map. 1.21.1 version.
Small space requirement, simple solutions, with hoppers, droppers, and a few observers.
For the sake of an example, I have added two more buttons in the following pictures and changed the code to 2025.
You can repeat any button without any problems. It will only be correct if it is pressed exactly after the next one in the sequence.
I hope you find it useful!