I really needed the header different in first page so temporary I tried to do something.
Here the result (It's a drive link cause I'm don't have enough access to post files):

https://drive.google.com/file/d/1wWn7q2n3jgBJuAuEr--cEtkEaQLI_e1X/view?usp=sharing

How I did it:

• I used the layout "web.internal_layout" for my report by inheriting
• In my inherited view I removed the header:
  xpath expr="//div[hasclass('header')]/div[hasclass('row')]" position="replace"
  
• In my report template I tried to create a "looks like" header.
  And then I put it in the body of my qweb report.

It's really not a good solution cause it's not the standard using of Odoo.

So I still need help if someone have a better solution

Thank you all,

Hello, Loic

If you place the header content directly as part of the report body, it will only appear on the first page. Obviously, this way it won't be a header. However, I think it will solve your problem without the need to use an external module.