The CKEeditor/TableToolsToolBar is not really a Drupal Modlue but an addon to the CKEditor.  At the current time it is listed that TableToolsToolBar is not ready for CKEditor5 but at the moment is is functional with Drupal 9 and CKEditor5.

It needs addition information if the json file to define where the libraries are for the addon.

    "repositories": [
       {
               "type": "package",
               "package": {
                   "name": "ckeditor/tabletoolstoolbar",
                   "version": "0.0.1",
                   "type": "drupal-library",
                   "dist": {
                   "url": "https://download.ckeditor.com/tabletoolstoolbar/releases/tabletoolstoolbar_0.0.1.zip",
                   "type": "zip"
                             }
                           }
       },

    "require": {
       "ckeditor/tabletoolstoolbar": "^0.0.1",

The purpose of the addon is to allow more arrangement of the CKEditor Toolbar,