The schema of the list on the SharePoint site has been modified and you will not be able to synchronize any pending changes to the SharePoint list. Schema changes are defined as columns being added or deleted, or modifying the data type or settings for an existing column in the SharePoint list.
If you choose to update or refresh the list, you will lose all pending changes and the Excel list will be updated with the current state of the SharePoint list, including all schema changes.
If you want to preserve any changes in your Excel list, you must click the Cancel button, which cancels the synchronization. You can then choose to publish the list and create a new list on the SharePoint site.