The PS2 hardware and uLaunchELF natively recognize only the FAT32 file system. Modern operating systems often format drives larger than 32GB as exFAT or NTFS by default. uLaunchELF cannot read these formats, resulting in an empty "mass:" directory.
Press the (or Cross, depending on your regional configuration) to enter the directory. ulaunchelf mass empty
Non-branded or "cheap" USB sticks ( TOSPLUS or cheap 128GB+ sticks) often fail. The PS2 hardware and uLaunchELF natively recognize only
Modern computers format storage devices using the scheme to support massive storage volumes. The PlayStation 2 hardware cannot interpret GPT structures. ulaunchelf mass empty
Often, the simplest "advanced" solution is just to update your software.