Slide Library

Slide Library was removed in SharePoint 2013 however this was not a popular decision.

User Voice
https://sharepoint.uservoice.com/forums/329214-sites-and-collaboration/suggestions/7081860-bring-back-or-replace-the-slide-library

Check out this support article for more details: https://support.office.com/en-us/article/Reuse-import-slides-from-another-presentation-c67671cd-386b-45dd-a1b4-1e656458bb86

Slide Library (Manual link required)
Use this link http://yourserver/sites/yoursite/_layouts/15/slnew.aspx?FeatureId={0be49fe9-9bc9-409d-abf9-702753bd878d}&ListTemplate=2100

Reference
http://techtrainingnotes.blogspot.com/2012/11/finding-missing-sharepoint-2013-slide.html

Third Party Solutions

http://www.teamsli.de/

https://www.iclickpoint.com/

https://accent-technologies.com/blog/2017/10/18/trying-find-replacement-sharepoint-slide-library/