These are added by the Content translation beta feature.

Someone gave me a solution to hide them, but it's a hack

.cx-contributions,
.mw-special-Contributions span h1 {
       display: none;
}

This is part of Content Translation beta feature (T88586). I can provide a little background about this specific feature, what it is intended to do, what it achieved so far, and possible next steps:

The need for a central place to start contributions
We needed a persistent place where to start a new translation with Content Translation. Instead of thinking on a specific one-off solution for translations, we thought it would make sense to provide a central place where users can start contributing different kinds of content (including translations). Currently in Wikipedia it is not clear in which ways you can contribute and how to do so (e.g., aspects such as constructing the URL of the page you want to create are barriers to contribution for many users). For a new user that created an account to fix a typo in an article, we want to be able to tell her "by the way, you can go here to contribute in all these possible ways", and provide a place where she can go again and again when she feels like contributing.

The use of "contributions" as a central place
When thinking on a central place to start new contributions, the contributions page seemed a natural fit: there is a list of your contributions and the new contribution controls are in charge of adding new items to that list. So conceptually, both parts seemed quite close. I understand that the current use of the contributions page is just for checking your current contributions, but I think that keeping the actions to create new contributions are more close conceptually to this place than other general places such as the sidebar.

User behaviour
When we tested these ideas with users, we got positive feedback. They were positively surprised that a gap to start contributing was filled and were able to use the prototypes successfully.

Once we launched the feature as part of Content Translation beta, we have been tracking its use and the data shows that these entry points are used. For users enabling the beta feature, 16% of the times a user visited the contributions page did so to start a new translation. While the main purpose of the page remains checking the list of contributions, a significant number of users seemed to chose it to create new content. In addition, from all the different entry points for CX, 88% of the accesses to CX were done through the Contributions menu and page actions.

So I think there is value in providing those actions and while consuming content is more common than contributing it, as we could expect, I think these entry points facilitate the creation of new content. So I'd not consider these "useless" as a general statement.

Ways to conciliate accommodate different needs

With all the above I'm not saying that this solution should work well for everyone as is. I really think it is important to identify those cases for which it does not work and avoid any disruption while still serving the users that benefit from this.

As a beta feature, we are still iterating on it and we encourage you to keep providing feedback and help us to find the right balance.
There are several things we can do to make the new entry point more compact. One idea we discussed some time ago was to make the actions in the contributions page more or less compact depending on the length of the contribution list. In this way, new editors with a short or empty list will have a clear way to start new contributions while advanced editors can still have access to it but consuming much less screen real state.

Thanks for the answer.
My main request is to be able to hide it in the Special:Contributions page, because I already find that the box for searching inside contributions is way too big (and not even collapsible...).
With the current output (Content translation + Search contributions), I almost see no contributions at all without first scrolling the page.

Please add a way to reduce all this, maybe like the legend that is collapsible in the Recent changes page ? And to keep the user choice between different sessions

Please add a way to reduce all this, maybe like the legend that is collapsible in the Recent changes page ? And to keep the user choice between different sessions

I created a task to describe the issue and explore possible solutions: T96200: Make contributions page actions more compact

Thanks for the feedback @NicoV

We should probably rethink this before starting to go out of beta, so I'm marking this as a blocker to T102107.