这是完全可行的，只要把问题一步一步来：

const array  = [
   { "Date;Department;Value": "2022-09-08;dept1;7856" },
   { "Date;Department;Value": "2022-09-08;dept2;9876" }
];

const result = array
  .map(Object.entries)           // Convert the objects to more easily accessible arrays.
  .map(([[k, v]]) => {           // Grab the key / value strings
    const keys = k.split(';');   // Split the keys into separate entries.
    const values = v.split(';'); // Split the values into separate entries.

    // Join the array of keys with the array of values, parsing numbers if possible.
    return keys.reduce((obj, key, i) => {
      obj[key] = isNaN(values[i]) ? values[i] : Number(values[i]);
      return obj;
    }, {});
  });

console.log(result);