Early 2009 MP with Mojave goes to black screen when trying to access boot options

I’m trying to get my MP recently updated to Mojave 2009 to get into the boot options screen so I can use the USB boot I made for Catalina per dosdude1’s instructions, but holding Alt doesn’t just shows a black screen that never changes and I have to restart the computer to load it to the normal desktop. Here is what I did recently:

firmware updated from 4.1 to 5.1
updated from El Capitan to Sierra then to High Sierra and I installed the HS firmware
then I updated the original 2.66 quadcore to a x5675 hexacore
RAM upgraded from 16GB 1066 to 32GB 1333
replaced the original radeon 4870 with a k600
then updated from HS to Mojave, no patching, just direct update

All 3 OS updates were in place, no fixes. My primary boot drive is a 480GB SSD which shows up as apfs in disk utility. About This Mac correctly recognizes all new hardware and everything seems to be working fine. I just can’t get to the screen I need to install Catalina. I assume a problem with the graphics card, or maybe I should have installed the Mojave patch? Any ideas are greatly appreciated at this stage.


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