It does this by hiding video recommendations and the ‘Shorts’ link on the front page, in addition to the ‘up next’ videos that appears when you watch a video, and the ads that are inserted in your search results. On iPad, it also hides comments.
When you want to see the hidden elements, you can toggle them on by tapping on the extension.
The app is open source and does not collect any data. You can inspect the source code, report bugs, and suggest additional features or improvements on: https://github.com/ulyngs/open-source-no-distractions-for-youtube
This update fixes a bug in the previous version that made the Up Next toggle disappear… it is now back! :)
Remember that the app is open source! You can flag bugs and submit ideas for improvement at https://github.com/ulyngs/open-source-no-distractions-for-youtube