The psxonpsp660.bin (often renamed or placed in specific subfolders) goes into the seplugins/popsloader/ directory on your Memory Stick.
, you typically need to place it in the specific "BIOS" folder of your emulator. Locate your Emulator's BIOS folder : For DuckStation, this is usually in Documents/DuckStation/bios Rename (If Necessary) psxonpsp660bin bios