Response times are different
34UC79G has 5ms(High), 1ms with Motion Blur Reduction
34UC79G-B has 14ms / 5ms GTG
34UC79G-B has these additional specs not mentioned by other
Pixel Pitch (mm) - 0.312 mm x 0.312 mm
Color Depth (Number of Colors) - 8bits, 16.7M
Refresh Rate - 144Hz (and yet the 34UC79G mentions it in its description page above the specs section so just ignore this difference)
Aspect Ratio - 21:9
34UC79G allows you to connect monitor to PC audio, -B doesn't
I think the 34UC79G id for people who want to use monitor for games/movies whereas 34UC79G-B might be for more professional users.
https://www.lg.com/au/it-monitors/lg-34UC79G-34-inch-curved-ultrawide-monitor
https://www.lg.com/us/monitors/lg-34UC79G-B-ultrawide-monitor