Access denied on external storage: application not found

I purchased an Android car head unit (K4811) and I cannot access a USB storage device that I plug in (32 GB, FAT32 or exFAT). I think that this comes from the absence of a program allowing elevation of rights, because by downloading FileManager+, when I select the USB key, I obtain this message: But if I click "OK", I get the error "Application not found": I tried from the Google "Files" application, it shows me that I have to "Tap to give File access": If I do, I get an "Access denied": If I click on the notification that appears when plugging in the USB key: This opens the basic file explorer in which the USB key does not even appear. Do you have any idea where this could come from? If an application allowing rights elevation is missing, is it possible to download it? I will be able to pass it by another means than a USB key. My goal is to access the files on an external USB storage key. EDIT ---- The application has storage access rights according to Android settings: