Yes, you can add a processing loading icon to indicate to users that the process is working in the backend when the ribbon button is clicked. Here are the steps to do this:
1. First, you need to create a custom web resource that contains the loading icon. You can use any icon that you like, but it's recommended to use a standard loading icon to make it more familiar to users.
2. Upload the custom web resource to Dynamics 365 by going to Settings > Customizations > Web Resources, and then click the "New" button to create a new web resource.
3. In the "Web Resource" form, give the web resource a name, such as "LoadingIcon" and set the type to "Webpage".
4. In the "Content" section, paste the HTML code for the loading icon. You can find many examples of loading icon HTML code online.
5. Save and publish the web resource.
6. Next, you need to modify the ribbon button to display the loading icon when it's clicked. To do this, go to the ribbon editor for the entity where the button is located.
7. Find the ribbon button that you want to modify, and then add a custom function to the "Command" section.
8. In the custom function, use the Xrm.Utility.showProgressIndicator() method to display the loading icon, and then call the backend process that you want to run.
9. Once the backend process has completed, use the Xrm.Utility.closeProgressIndicator() method to hide the loading icon.
By following these steps, you should be able to add a processing loading icon to indicate to users that the process is working in the backend when the ribbon button is clicked.