Add "joomla/data": "~4.0" to the require block in your composer.json and then run composer install.
{
"require": {
"joomla/data": "~4.0"
}
}Alternatively, you can simply run the following from the command line:
composer require joomla/data "~4.0"If you want to include the test sources, use
composer require --prefer-source joomla/data "~4.0"