PT 2020.5 not installing

[dowd]

Hey guys,
I'm having problems installing PT 2020.5. I've recently upgraded a Mac Pro5,1 mid 2012 to a more modern machine using the following parts

OS Mojave 10.14.6 on SSD with a second HD running High Sierra 10.13.6
dual Intel X5680 Xeon - 2x6cores, 12 threads @ 3.33GHZ .
Memory 6GB 1333 MHz DDR3 (6x1 GB cards)
AMD Radeon HD 7950 with 3GB Vram - this is an updated ‘metal’ compatible GPU flashed for Mac Os. Recommended by Apple. I spent an great deal of time researching on You Tube and the Apple site to obtain compatible parts. Nested deep within the Avid support page I later found a reference that says ...and I quote 'MSI Radeon RX560 required when using macOS Mojave. Other graphics cards have been shown to cause errors in Pro Tools.' Of course I found this after purchasing the 7950. The 7950 works perfectly with High Sierra and 2020.5 but when i try to install PT on the other hard drive with Mojave I get the spinning ball of death and have to restart. I should have realized something was up because when I initially installed 2020.5 the installer refused to make the Mojave drive available and I was only able to install on the high sierra drive. I suspect I will have to fork over for a RX560. Just wondering if anyone else has managed to bypass this issue or has any advice to offer...Thanks guys pd