What potential issues can arise when upgrading from PHP 7.4.22 to PHP 8.0.9 in terms of code compatibility?

One potential issue when upgrading from PHP 7.4.22 to PHP 8.0.9 is the deprecation of the "real" data type, which is no longer supported in PHP 8. To resolve this, you should update your code to use the "float" data type instead.

// Before PHP 8.0.9
function calculateSum(real $num1, real $num2) {
    return $num1 + $num2;
}

// After PHP 8.0.9
function calculateSum(float $num1, float $num2) {
    return $num1 + $num2;
}