Intel Core i3 9100 's Advantages
Better graphics card performance
Higher base frequency (3.6GHz vs 2.5GHz)
Intel Core i5 12400 's Advantages
Released 2 years and 9 months late
Higher specification of memory (4800 vs 2400)
Larger memory bandwidth (76.8GB/s vs 37.5GB/s)
Newer PCIe version (5.0 vs 3.0)
Larger L3 cache size (18MB vs 6MB)
More modern manufacturing process (10nm vs 14nm)