Le site steamwalletgift.com est-il sûr ?

Completely fake. Obviously this website is attempting to copy Steam's official design (and doing it well tbh) and when you click on links such as "About Valve" at the bottom of the page, it just redirects you to the official site. When you hit enough points, the code is hidden behind an adwall. It's very unlikely that you will be able to get past this, and generally any website trying to copy an official one is fake. TL;DR: When it's too good to be true, it's probably fake.

I am very skeptical about this site. According to them, you earn points by sending people a link and use the points to get a Steam card. However, when doing research for this site, I saw a video discussing a different site using the same gimmick, and how that site was a complete scam. I have not tried this site nout yet nor have I seen any reviews pertaining to this site specifically, but if that other site which has the same "rules" is a total scam, then I am inclined to suspect that this is too.