Boot Manager Can't See Sequoia Boot Disk (USB External Hardisk) Made by OpenCore Patcher

Hi Apple friends, macOS Sonoma's (w/ OpenCore Patcher) boot manager can't see Sequoia boot disk (USB external hardisk, an extra hardisk I use to create OpenPatcher boot disk. I was successful using this setup for macOS Sonoma w/ OpenPatcher) made by OpenCore Patcher even though Disk Utility says the Sequoia boot disk made by OpenCore is bootable. I'm pressed the Option key for the Boot Manager to show the Boot EFI but it still can't see the boot disk.

This is on an Late 2015 5k iMac (it has Metal). Is it because it's on external hardest? I do have an SSD or does the OpenPatcher 2.0 now only works with flashdrives?

Thank you in advance.

God bless all Apple users.