Nvidia Quadro K6000

Do you have the Quadro K6000 already in your MacPro. It looks like it will work in Mojave and Catalina.

Please read this, https://www.tonymacx86.com/threads/will-my-nvidia-graphics-card-work-with-macos-list-of-desktop-cards-with-native-support.283700/ and do any further research. If you haven't got the card yet then make sure you buy a Mac Edition card or 'flashed' for mac card.

As your MacPro is from 2009, it cannot officially install Mojave. Please read Section 1 in the next link and check the list of recommended cards, How to upgrade to macOS Mojave - Apple Support

A MacPro from 2009 is known as the 4.1, it's firmware can be upgraded so it effectively becomes a 5.1 (2010-2012 MacPro)

you will need to search the internet on how to do that. If you have done that then you can install Mojave.

If you want to keep it identified as a 4.1 then there are methods for getting 'Mojave on unsupported macs'.

Is the X5690 the graphics card and is it a Metal capable card.