The core_version_requirement key in info.yml file
The core_version_requirement key specifies what versions of Drupal that the module is compatible with.
name: Exampletype: modulecore: 8.xcore_version_requirement: ^8 || ^9
The above example says that the module is compatible with Drupal 9 and Drupal 9. Notice that the core key is still compulsory here
The chnage
After Drupal 8.8.0 we will not need the core key anymore.