The drive is FAT32 (which Android reads fine), but the partition is flagged as "Hidden" or "Non-Mountable" by USBUTIL. Fix: On Windows, use DiskPart to clean the drive and start over. Do not use the "Hidden" feature in USBUTIL if you intend to use the drive on Android.
can read. While traditionally a Windows application, you can now manage this entire process directly from your device. What is USBUtil? usbutil ps2 android
on the root of your FAT32 USB drive and drop the ISO inside. Comparison: Emulation vs. Hardware Play Using USBUtil on PS2 with Android: A Guide
Android’s built-in formatter often creates a "Removable" drive with GUID Partition Table (GPT) instead of MBR. The PS2 OPL only reads MBR. Fix: Use an app called Partition Table Editor on Android. Change the partition style to MBR (Master Boot Record) and format as Primary FAT32. File 1: UL
UL.ISO_NAME.00UL.ISO_NAME.01