Hi,
There are 3 things you could use here:
1. Once you select the original source of the launch, you can use the "Compare to Source" option, which will provide a visual representation of the changes made, but this is on a page-by-page basis. Still, this can be useful
2. When you use the "Promote Launch" option (see the above image), you can select only the pages that were modified. This will show all pages that have changed compared to your original source.
3. You can use the Timewrap option to see the updates by date. You can refer to this link for more details: https://experienceleague.adobe.com/en/docs/experience-manager-cloud-service/content/sites/authoring/...
So I think once you know which pages were modified using option #2, you can check further details via option #1 or #3. If you only want a page count, then the option #2 should work
Hope this helps
Esteban Bustamante