Your GT 210 is not Metal II capable which is a Mojave requirement for graphics. High Sierra works with a GT 210 but not Mojave. The 210 doesn't meet Metal II requirements. You could switch to a GT 710 which works with HS and Mojave. There is only the APFS option for the Mojave file system. It's possible to update and switch back to HFS+ but it's a lot of hoops to jump through after each update.
From Apple's official statement of graphics cards for use with the 2010-12 Mac Pro
These are the cards that support Metal and are compatible with macOS Mojave:
- MSI Gaming Radeon RX 560 128-bit 4GB GDRR5
- 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 has also listed the following graphics cards that “might also 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