The only way I can see to edit a grid after its placed is to edit the classes in the source. I am unable to select the grid from ckeditor and reopen the settings dialog.
I'm encountering the same issue. I can create the grid element in the WYSIWYG editor, but I can't edit it afterward—the Edit button isn't available. This problem seems related to Drupal core 10.5.x, which updated CKEditor 5 to version 45.2.0.