Hello John, thank you for reaching out to the Microsoft Community. I'm here to help with your questions or issues. Just note – this is a place where passionate Microsoft users help each other, we don't work directly for Microsoft.
Just to make sure I got it right, the main issue is that your Mac is trying to authenticate with your Dell Optiplex using a traditional username and password, but your Dell is currently configured to use a PIN for login.
The simplest solution, as you suggested, is to reset your Windows password. This would enable you to use the new password for the SMB connection from your Mac.
If you prefer to keep using your PIN for logging into your Dell, you can enable password login as an alternative. On your Dell Optiplex, go to "Settings," select "Accounts," then navigate to "Sign-in options." Under "Password," click "Add" and set up a new password. This password can then be used for the SMB connection from your Mac.
I hope this helps! If you have any more questions, feel free to ask.