A c02 cartridge just won't cut it for a fat bike tire. You need one of these. A pain to carry, but really works well with fatties.
https://www.amazon.com/Lezyne-FLOOR-MICRO-DRIVE-HVwGAUGE/dp/B0747VCK3G/ref=sr_1_1?dchild=1&keywords=lezyne+fat+tire+pump&qid=1609763058&sr=8-1