You need to somehow get OCLP 3.0.0 (nightly) on your mac. Your mac is the last MacPro to have this issue. 2.5.1 doesn't have the USB maps for Tahoe. What you need is the following:
Note: this is really techy, and will most likely download stuff that you will never use again.
You need to get Python 3.11 or newer installed on your mac (or, if you just have Tahoe on it, you need another mac that has I think it's macOS (10.13.6) High Sierra or later.) download python
here.
Go to
Dortania's macOS-next branch
Click on code and click download zip. In the downloads folder open the zip (if it doesn't automatically open) and then open the terminal and run pip3 install --upgrade pip && pip3 install -r "~/Downloads/$(ls -d ~/Downloads | grep '*macos-next*')/requrments.txt" Note: you have to be connected to the internet.
What do those commands do? The first one upgrades python's pip, which is basically its installer. The second one installs the components that OCLP requires to run without being compiled (which is the state of being a .app or executable binary)
Now if these have run properly open the opencore folder and click double click on OpenCore-Patcher-GUI.spec, not OpenCore-Patcher-GUI.command. It should open in TextEdit
Now press ⌘ + F and type "universal2" it should only show one option. Replace it with "x86_64" then press ⌘ + S and close TextEdit.
Now, open the terminal and type cd, then in finder navigate to ci_tooling and drag the privileged_helper_tool folder into the terminal window. Back in the terminal press the right arrow key and hit enter. Then type make debug if prompted to install commandline tools, go though with the install, then run make debug again.
Now, back in the opencore folder open the Build-Project.command file and let it run in the terminal. Make sure that you allow it to run if prompted.
When it is done open the dist folder that it generated and and copy OpenCore-Patcher.pkg onto a USB drive.
Back on the 5,1, plug in a USB2 Hub and connect your keyboard and mouse into it. Now you can navigate the interface.
Plug the USB drive into your mac and open it in Finder. Open the Pkg file that you put on it and install opencore. Now you can open opencore-patcher and install root patches.
Note: I am impressed that you got Tahoe installed with OCLP 2.5.1!
Note: yoy also need the KDK, which you can get
here, just scroll through the releases until you find the one that is exactly or close to the version of Tahoe that you have. Put it on the USB drive with the OpenCore-Patcher installer.