Many thanks.
My mistake was to save as bookmark a QR page different from the home page.
It looked similar but did not have the flight search option, only proposed a flight booking based on my previous search, without the Manage/check in tab.
And when I clicked on the main book tab in the upper part of the page, it did not offer to book a new flight (just flight schedule, hotels, etc...).
I did not realize that I had to simply click on the QR icon.
Anyway, I changed my bookmark. Many thanks.