Anything that prevents you from playing the game properly. Do you have issues playing for the game, downloading it or successfully running it on your computer? Let us know here.
Any suggestions for a graphics card that will run Factorio at its highest settings?
The card should cost under £100/$100 and passive cooling would be good.
If you want to play on higher resolution monitor, you might need something more powerfull, for 4K something with PassMark score 8000 or higher, I'd say.
(Note: I consider High quality texture compression to be highest reasonable setting, setting it to None will give slightly better quality with completely unreasonable performance penalty, and VRAM requirement skyrocketting through the roof)