The SfdcUsername and SfdcPassword properties do not accept their values from an input field.
Node properties that support this mode of operation have a '(from Field)' source option in the header of the property, for example see the Query property in the screenshot below. The drop-down control enables you to set the source as a literal (the default) or select the from Field variant. In this case the SOQL query string will be sourced from the value in the Statement field.

You can parameterize the SfdcUsername, SfdcPassword, etc properties using Run properties (or Data Flow properties) - as indicated in the above example by the property references. Note that it is preferable to use a Run property for the password rather than a Data Flow property if the data flow is to be shared with other users on the same system (e.g. Server instance) as the password value would still be accessible to the other users.