Solidity example to show that calldata is read-only and cannot be modified.

AllAboutCalldata.sol

pragma solidity ^0.8.0;

contract AllAboutCalldata {

    function manipulateMemory(string memory input) public pure returns (string memory) {
        // you CAN  modify arguments passed with data location 'memory'

        // you can add data in the string
        input = string.concat(input, " - All About Solidity");

        // you can change the whole string
        input = "Changed to -> All About Memory!";
        return input;
    }

    function manipulateCalldata(string calldata input) external pure returns (string calldata) {
        // you CANNOT modify arguments passed with data location 'calldata'

        // you cannot add or edit data in the string
        // TypeError: Type string memory is not implicitly convertible to expected type string calldata.
        input = string.concat(input, " - All About Solidity");

        // you CANNOT change the whole string
        // Type literal_string "..." is not implicitly convertible to expected type string calldata.
        input = "Cannot change to -> All About Calldata!";
        return input;
    }
}