Help! I can’t update macOS on mid 2012 Mac Pro 3.06 GHz 12 core

I can’t update my Mac Pro High Sierra even though it has an NVIDIA Quadro K5000 4096 MB which is on the metal list. For some reason the update won’t recognize it as acceptable. Any thoughts on how to fix this and/or is there a better graphics card I should get?

Also.... I hate the idea of the Trash Can and having my 3 other drives external. Is there any hardware upgrade to my existing Mac Pro to make it perform as well as the 2013 Trash Can?

Thanks