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.