Just ads, not sponsored content, but those extensions you speak of aren't a thing on the AppleTV. I can see were the popular parts of the video are, usually just going to the next spike will be the end of the sponsored segment. I haven't found it to be a big deal. The ads, that abruptly interrupt the video, and make you wait for several seconds before you can skip (if you can skip at all) are the things that bug me the most. Sponsorship are minor in comparison. Plus, the better YouTubers will work it into their content, so I may not want to skip it.

no. YouTube Premium does not block sponsored content.