If you're building a GAMING PC, then you don't want an APU, you want a CPU and discrete video card. If you want a PC to play casual games on, then you want the 2400g. As you can see from Extremetech's review of the 2400g, in actual games, even several years older games, it is not capable of 60fps at 1920x1080, and in some games isn't able to do 60fps at 1280x720.
https://www.extremetech.com/computing/263683-amd-ryzen-5-2400g-review-best-blend-cpu-gpu-performance-weve-ever-seen