Hey @Bastien_81488 🙂 Welcome to the 3 Community!
While you are roaming if there are any other networks available, other than Orange F and SFR which you have already attempted, I would recommend testing all available networks and restarting your phone in between selecting networks to check which network works for you.
If this doesn't work then I would recommend going here and selecting your device. Once you have selected your device, under network you can find "How to change network settings" and try switching between 3G and 4G manually to check which works for you.