Note: PS2 USB ports are USB 1.1, which causes slow loading times and potential stuttering in video cutscenes. If you'd like, I can:
Follow the on-screen instructions to install Free McBoot onto your PS2 memory card. Playing Games from USB: Mcboot Download Usb
Used to launch the installer on an unmodified PS2. Note: PS2 USB ports are USB 1
Help you find a (no download needed)
For formatting USB drives larger than 32GB to FAT32. General Installation Steps: Mcboot Download Usb
Create a folder named DVD on your USB drive and place your ISO games there.
Open the Open PS2 Loader (OPL) app from the Free McBoot menu to launch your games.