JavaSript: Why is my code modifiying an array of objects on the original data object?

Question

I have this code that is supposed to avoid modifying the original data object "info" array of objects but it does! despite it is processing copies of this array?! I need to keep the original data object intact as otherwise, I am getting continually modified data object with each call of the functions as if they are chained together?!

    const data = {
    owner: "John Doe",
    info: [
      {
        employeeId: 123000456,
        firstName: "Alex",
        lastName: "Mckenna",
        email: "alex@work.org",
        salary: 48000,
        department: "Art and Media",
      },
      {
        employeeId: 123000777,
        firstName: "Devon",
        lastName: "Foley",
        email: "devon@work.org",
        salary: 75000,
        department: "Advertising",
      },
      {
        employeeId: 123000894,
        firstName: "Riley",
        lastName: "Couch",
        email: "riley@work.org",
        salary: 33000,
        department: "Shipping",
      },
      {
        employeeId: 123000533,
        firstName: "Cara",
        lastName: "Eramchuk",
        email: "cara@work.org",
        salary: 39000,
        department: "Accounting",
      },
      {
        employeeId: 123000721,
        firstName: "Cole",
        lastName: "Tilbury",
        email: "cole@work.org",
        salary: 43000,
        department: "Accounting",
      },
      {
        employeeId: 123000832,
        firstName: "Bree",
        lastName: "Northam",
        email: "bree@work.org",
        salary: 61000,
        department: "Shipping",
      },
      {
        employeeId: 123000271,
        firstName: "Mark",
        lastName: "Miller",
        email: "mark@work.org",
        salary: 55000,
        department: "Sales",
      },
      {
        employeeId: 123000442,
        firstName: "Jenna",
        lastName: "McEvoy",
        email: "jenna@work.org",
        salary: 40000,
        department: "Sales",
      },
    ],
  };
  

const myCompany = {
  renameProp(arr, old, neu) {
    const modified = arr.map((obj) => {
      if (old in obj) {
        obj[neu] = obj[old];
        delete obj[old];
        return obj;
      } else {
        return `property, ${old}, doesn't exist for employee ${obj["firstName"]} ${obj["lastName"]}`;
      }
    });
    return modified;
  },
  sortCopy(arr, prop) {
    try {
      const copied = Array.from(arr);
      copied.sort((a, b) => {
        if (typeof a[prop] === "string" && typeof b[prop] === "string") {
          if (a[prop].toLowerCase() > b[prop].toLowerCase()) return 1;
          else if (b[prop].toLowerCase() > a[prop].toLowerCase()) return -1;
          else return 0;
        } else {
          if (a[prop] > b[prop]) return 1;
          else if (b[prop] > a[prop]) return -1;
          else return 0;
        }
      });
      return copied;
    } catch (err) {
      return err.message;
    }
  },
};

console.log(myCompany.renameProp(data.info, "salary", "wage"));
console.log("\n\n", myCompany.renameProp(data.info, "firstName", "name"));

console.log("\n", "examples of second function: ", "\n");

console.log(
  "sorted by employeeId: \n\n",
  myCompany.sortCopy(data.info, "employeeId")
);
console.log(
  "\n sorted by first name: \n\n",
  myCompany.sortCopy(data.info, "firstName")
);

console.log("\n\n original array \n\n", data);