A child theme is identified by WordPress when there is a directory (for example child-theme) inside /wp-content/themes/ with the following files:
style.css
This file must start with a comment template like this:
 /*
 Theme Name: Example Child
 Author: Me
 Author URI: https://example.com/
 Template: example
 Text Domain: example-child-theme
 Domain Path: /languages/
 */
The most important things to consider here are:
The Template name must be exactly the folder name which holds the parent theme (aka the parent theme slug)
Name your child theme in such a way you can easily identify it in Dashboard (usually just append Child to the parent's name, like Example Child)
index.php
functions.php