Last week working on a project, I needed to list Recent Events in the sidebar as widget for a custom post type CPT, although there are few plugins but none provided the thumbnails for CPT, so I authored the plugin with required features and have now published both on WordPress and GitHub.
The Recent CPT Widget Thumbnails plugin allows you to display a list of the most recent posts, cpt from all or a specific category or tag, shows the post title, excerpt & thumbnail.
Download or install from here Recent CPT Widget Thumbnails WordPress Plugin.
Here is the link of Recent CPT Widget Thumbnails WordPress Plugin GitHub repository.
Hope that helps.