From https://bbaovanc.com/blog/youtube-url-structures-you-should-know/#isso-109:

Anonymous•3 months ago

No documentation of "&pp=" extensions to YouTube links in this post.

&pp= indicates what you searched to net that result, the following text jargon is Base64 and contains the search query.

I'm intentionally writing this in here so you get more traffic of people trying to figure out what that is and why it's there. I'm not trying to be mean, I just need to share answers and they are not currently easily available without googlefu. If you could update this with that information, that would be very lovely.

Need to research and find good sources (or test myself) to know what it does for sure. Just to make sure there aren't any inaccuracies in their comment.

Modifies content/blog/youtube-url-structures-you-should-know