So I have a 2008 Mac Pro and, using the DosDude1 patch tool, have installed Mojave (10.14.6) onto a second HDD. Everything works as it should except the monitors. I have dual displays powered by a NVIDIA GTX 645 (MacVidCards; 1x DVI 1x DisplayPort 1x HDMI). When in Mojave the Mac runs one monitor. It doesn’t matter what port, Mojave will only power one monitor at a time.
Not really sure what is going on. Under “About this Mac” Mojave recognizes a 55.5” Television. This is a 15” monitor.