Exactly How and Where Does The Trending Posts System Work Inside A Server?

I know this question is fairly simple for you and there are many related answers but none of them explain all what I need.

So you all must have been to YouTube, there you must have seen the Trending Posts Section, where all the videos which have the most views/likes/dislikes (I don't know exactly) w.r.t the time are listed. Now, all those videos are from different different channels.

I want to know:

1. There must be an algorithm or function inside the server to do that? If there is one, then when do it runs, i.e, are the results kept ready inside the server the same a google search engine --- which keeps the pages stored according to their ranking and whenever someone searches it delivers the result.

2. The above algorithm goes through every posts, right? But when? How does it knows that this post from this youtuber is getting this amount of views or a lot of views.

3. Now, after it knows which posts are trending --- where are they stored. Like, if we take mongodb database. Is it kept in a different collection like trending posts or their id's

I know the above questions must be confusing because of my half(or no) knowledge. But, please let's help me know it all. I am trying to get this answer for a very long time. Any guides or tutorials appreciated. Thanks!