Jquery not loaded by default in wordpress 5.6

You can ensure that jQuery is loaded by adding it to the $dependencies array when you enqueue your script.

add_action( 'wp_enqueue_scripts', 'wpse384152_enqueue_my_scripts' );
function wpse384152_enqueue_my_scripts() {
    wp_enqueue_script( 'my-script', '/path/to/my/script.js', array( 'jquery' ) );
}

That will ensure that a) jQuery gets loaded and b) it gets loaded before your script.

References

• wp_enqueue_script()
• Default scripts