“SponsorBlock is an open-source crowdsourced browser extension and open API for skipping sponsor segments in YouTube videos. Users submit when a sponsor happens from the extension, and the extension automatically skips sponsors it knows about. It also supports skipping other categories, such as intros, outros and reminders to subscribe.”
– From the Sponsorblock website
Sponsorblock is supported in FreeTube as of v0.13.0. You can find the option to enable it at the bottom of the settings page. At this time, you can enable / disable Sponsorblock, as well as change the API URL that FreeTube points to if you’d like to use a different server.
We, the FreeTube Team, consider user privacy to be our top priority. While the majority of advertising methodologies tend to be invasive of users’ privacy, sponsorships (or sponsor segments) within videos is one of the few methods that do not prey on users in this regard. For that reason (as well as due to its recent and well-deserved popularity), we encourage content creators to utilize this method of advertisement and users to allow their own exposition to sponsorships in their service using habits, so that privacy-friendly methods of advertisement can continue to thrive in this community. If creators end up deciding that this is not an optimal way of advertising, then it will only encourage more privacy-invasive advertising, among other things.
Despite all of that, we’ve collectively decided to allow the inclusion of this feature, so that users can have the privilege of choice, since we don’t intend to force our beliefs onto anyone.
We do, however, hold the responsibility to state this: We highly encourage users to keep this feature disabled
For more reading about this, please check out the response made by the NewPipe Team on the same issue.