
Apple's new macOS Mojave update is not compatible with mid-2010 and mid-2012 Mac Pros with stock GPUs, but it is supported on 2010 and 2012 Mac Pro models that have been upgraded with graphics cards that support Metal.
Apple today shared a new support document that provides a list of graphics cards that are Metal-capable, which will be useful for 2010 and 2012 Mac Pro owners who want to purchase a new graphics card to upgrade to macOS Mojave.

According to Apple, the following graphics cards are known to be Metal-capable and compatible with macOS Mojave on the mid-2010 and mid-2012 Mac Pro models:
[*]MSI Gaming Radeon RX 560 128-bit 4GB GDDR5
[*]SAPPHIRE Radeon PULSE RX 580 8GB GDDR5
[*]SAPPHIRE Radeon HD 7950 Mac Edition
[*]NVIDIA Quadro K5000 for Mac
[*]NVIDIA GeForce GTX 680 Mac Edition
Apple also lists other AMD graphics cards that "might" be compatible with macOS Mojave:
[*]AMD Radeon RX 560
[*]AMD Radeon RX 570
[*]AMD Radeon RX 580
[*]AMD Radeon Pro WX 7100
[*]AMD Radeon RX Vega 56
[*]AMD Radeon RX Vega 64
[*]AMD Radeon Pro WX 9100
[*]AMD Radeon Frontier Edition
You can check to see if your graphics card is compatible by holding down option while selecting Apple logo to access System Information. Under Graphics/Displays, if "Supported" is listed next to the Metal entry, the graphics card will work with macOS Mojave.
According to Apple, once a Metal-capable graphics card has been installed in a 2010 or 2012 Mac Pro, macOS Mojave can be downloaded and installed after turning off FileVault.
Article Link: Apple Outlines Metal-Capable Cards Compatible With macOS Mojave on 2010 and 2012 Mac Pro Models