Unable to boot from OCLP-created USB Installer for macOS major upgrade.

Current Configuration:

Mid 2012 15" MacBook Pro (MacBookPro9,1), 16 GB RAM, 1 TB SSD, Monterey 12.7.6, OCLP 2.4.1

This configuration has been running smoothly with no issues for 1.5 years.

Using this set of instructions for performing a macOS major upgrade from macOS 12 to macOS 15:

https://dortania.github.io/OpenCore-Legacy-Patcher/UPDATE.html#major-upgrades

and

https://dortania.github.io/OpenCore-Legacy-Patcher/BOOT.html

Per above instructions: From within OCLP, used "Create macOS Installer" menu option to download Sequoia and create a USB flash drive installer.

Problem:

Normally, on a restart, the EFI boot picker briefly appears before continuing with the normal boot.

For upgrading: With installer inserted into a built-in USB port, the USB installer should appear on the EFI boot picker, but in THIS case, the Installer does not appear. Holding Option on a subsequent restart brings up the STANDARD boot picker with EFI being one of the options. Selecting EFI then takes you to the EFI boot picker with Monterey being the only one shown. USB Installer is ignored and does not appear, even when hitting the space bar to bring up the hidden boot picker options.

Additional Notes: Launching the "Install macOS Sequoia" application BOTH from the Applications folder in Finder AND the OCLP created USB installer both launch the installer normally with no errors.

I am hesitant to install from Finder as the above linked instructions specifically advise against doing that.

I wanted to check with the community before I just wipe the drive and start from scratch (Catalina fresh install followed by standard OCLP install of Sequoia). This is the way I have done it on over a dozen various machines (from clean install - never done an upgrade of an already OCLP installed macOS).

Suggestions?

Thanks in advance.