Hey Romuald712,
Thanks for posting in Apple Support Communities. Let's work together to find out where this storage information is coming from. To double check your storage info, we'd need you to connect your iPhone to a computer. It can be a Windows computer with iTunes or a Mac running macOS with Finder. See this article for more information: How to check the storage on your iPhone and iPad
Use the Finder or iTunes to check the storage on your iOS device
1. On a Mac with macOS Catalina 10.15 or later, open the Finder. On a Mac with macOS Mojave 10.14 or earlier, or on a PC, open iTunes.
2. Connect your device to your computer.
3. Select your device in the Finder or in iTunes. You'll see a bar that shows how much storage your content uses, divided by content type.
4. Move your mouse over the bar to see how much storage each content type is using.
Once you have that information, let us know if it shows the same amount of storage information as it does on your iPhone settings.
Cheers!