Hi there,
The number of thumbnails shown in the digital object carousel is tied to the Global results per page setting in Admin > Settings > Global. See:
By default this is set to 10 results per page, but can be updated. Keep in mind that at present, this is a global setting - so it will also affect number of search/browse results per page and any other list results that are paginated for performance.
Similarly, be aware: increasing this value can impact performance, as more page resources need to be loaded before the browser times out. So: if you set this too high, it could cause issues.
Note that user can always click the "Show all" link in the carousel to see all results:
Cheers,