Drupal 9 compatibility

What needs to be done to make this module compatible with Drupal 9? There is a drupal-check tool that can help uncover deprecation issues

When I ran drupal-check it didnt seem to detect any errors, so maybe all that need to be done is the composer.json change mentioned above.

Here's the output when I run drupal-check against 8.x-1.2 in my Drupal 8.8.5 project root:

$ drupal-check modules/jquery_ui_draggable//
 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%
                                                                                                   
 [OK] No errors

If the module is already D9 compatible, maybe the maintainer can fill out the necessary text field to show the D9 Compatible badge on the module's home page under "Project Information"