OK, I tried again to reach the support about this problem. Because if the hack is perfect, hte next update wil erase it. I don’t want to watch to put it back each time.*
The support spent some time and finaly gave me an answer and a solution :
“I can confirm that this happens because the “News” page is not assigned as your Posts page.
Currently, the News page is just a regular WordPress page, so the next page will use “/2” as the next page link instead of “/page/2” (which is only used for WordPress’ Posts page and archive pages). If you really wish to use “/page/2” as your pagination link, you will need to do the following:
1. Edit your news page, and save it as a template (https://elementor.com/help/save-page-as-template/).
2. Go to Settings > Reading, and set “News” as your Posts page.
3. Since the News page will become an archive page for your posts, it cannot be directly edited with Elementor. To customize this page, kindly go to Templates > Theme Builder, and create an Archive template.
4. Import the template you just saved into the Archive template you have created.
5. Change the Posts widget’s query to “Current Query”.”
It works… but only to display ALL the posts.
I could find a way to display a specific category :
1. Edit your news page, and save it as a template (https://elementor.com/help/save-page-as-template/).
2. No need to go go to Settings > Reading, and set any page.
3. Then go to Templates > Theme Builder, and create an Archive template.
4. Import the template you just saved into the Archive template you have created.
5. Choose as condition one or several post categories
6. Change the Posts widget’s query to “Current Query”.
7.Then pagination works.
8.It seems that to set the number of post to display, you must to Settings > Reading.