If your goal is to watch a video that was recently made unlisted or private, a browser extension bring it back. But the Wayback Machine (Internet Archive) can.
: Available for Firefox, this extension aims to restore the dislike counter and provides a "quicker method" for discovering unlisted content.
To access unlisted videos on YouTube, you'll need a browser extension that can bypass YouTube's restrictions. One popular extension that allows you to see unlisted videos is called "Unlisted Videos Viewer" or "YouTube Unlisted Video Viewer." These extensions work by: see unlisted videos youtube extension
However, certain extensions and tools can help you find unlisted videos using legal, open-source intelligence and archiving methods. How Tools and Extensions Actually Find Unlisted Videos
Finding the right tool depends entirely on your goal. Here is a curated list based on the current landscape. If your goal is to watch a video
agervold/youtube-relist: A Chrome extension for displaying ... - GitHub youtube-relist. Lists youtube videos that are unlisted.
Instead of hunting for a magical extension, consider: To access unlisted videos on YouTube, you'll need
A userscript that helps add videos from playlists and search results to a list. It is designed for "combining multiple lists and filtering out videos that are already archived". This is a niche tool for data management, not broad discovery.
While some are standalone extensions, others are web-based platforms that offer browser-integrated features: