Take a screenshot of a new tab using Puppeteer

I’m using puppeteer to click on a link that opens a new tab, and take a screenshot of this tab using :

const pages = await browser.pages()
const new_page = pages[pages.length-1]
await new_page.screenshot()

but I made some research and I found that browser.pages() contains only the default blank pages and my current tab but not the new one.

Hence, when I take a screenshot, it takes a screenshot of the current tab.
To give you some context, the new tab is a PHP url and it display a pdf file. I tried waitForNavigation, bringToFront and nearly every possible console.log().

Does anyone know how to help me ?