^This is correct. Get rid of the source: ‘item’ param, run a search and add the results to select options: In this example, returnValidUsers() just runs a search and returns the results as an array

var userSelect = form.addField({
                    id: 'login_user_id',
                    label: 'User',
                    type: serverWidget.FieldType.SELECT,
                }).updateBreakType({
                    breakType: serverWidget.FieldBreakType.STARTCOL
                });

                var results = returnValidUsers();

                userSelect.addSelectOption({
                    value: '',
                    text: '--SELECT--'
                });

                for (let i = 0; i < results.length; i++) {
                    userSelect.addSelectOption({
                        value: results[i].getValue("custrecord_employee"),
                        text: results[i].getText("custrecord_employee")
                    });
                }