Added:
- Compatibility with TYPO3 v12 (15)

Changed:
- Form type from "CountrySelect" to "ExtCountrySelect" (15)

Updated:
- symfony/intl to version 6.2.8 for non-Composer installations

Removed:
- Compatibility with TYPO3 v11

Have also a look into the Migration chapter of the documentation:
https://docs.typo3.org/p/brotkrueml/form-country-select/3.0/en-us/Migration/Index.html