wp_get_environment_type is undefined

It is a core WP function, but only after WordPress version 5.5.0.

If you’re using an older version of WordPress, it won’t exist yet.

Do this:

add_action('admin_init', function() {
if ( ! function_exists( 'wp_get_environment_type' ) ) {
    return;
}
$environment = wp_get_environment_type();
//...

Or, better still, make sure your WordPress installation is up to date.