Because they want you to watch shorts. They know that people who watch shorts are the most brainrotted on the platform, and the ones who will keep scrolling and watching video after video, and seeing ad after ad, and those are the users YouTube wants all other users to be like.

And so they will push shorts in your face again and again no matter how much you say no, because they think eventually they'll break you.

The close button is just a temporary placebo to make it feel like you're the one in control.

Blocks shorts.

uBlock filters use a modified form of CSS selectors to determine what parts of a page to hide.

If you know vaguely how CSS selectors work you can infer that the filter definition is matching on youtube.com and is finding an element whose title property is shorts - so it seems to be doing an appropriate thing.

The important part is that uBlock filters are not executable; you can't inject malicious code through one, as they are simply patterns which describe what parts of a page should be hidden, and hiding content is all they can do.

The worst that a filter could do is hide something that shouldn't be hidden.

It removes short-videos from the main page and search results, as well as removing the link from the menu.

It removes shorts ig

Do I add it in My filters?

Yes.

I wrote that myself, using Firefox on macOS, it might not work in other browsers (though it should generally work in firefox across platforms). It probably doesn't work on mobile.