Select Radio Checkbox Field HTML 5 Validation
This module adds HTML5 validation to required select, radio, and checkbox fields in Drupal. It addresses a core limitation by automatically enabling this validation for these field types.
This module providing HTML 5 validation for Select, Radio, and Checkbox field types. When these field types are required. This module helps those people they are using core HTML 5 validation in his/her projects.
When you installed a fresh Drupal 8 Setup. Core Drupal 8 is not providing HMTL 5 validation for Select, Radio, and Checkbox field types. After installing this module. Your problem will solve. This module automatically will add HTML 5 Validation for Select list (box), Radio, and Checkbox field types.
Learn more why HTML5 validation is bad here: https://www.drupal.org/node/1797438
Install it like any other module
composer require drupal/s_r_c_html5_validation