1440p CPU
A solid choice would be the Ryzen 7 5800X3D or Ryzen 7 5800X. Both offer strong performance for 1440p gaming.
A newer generation is needed for better performance. A 3300x or 3600 would work well.
I'm just hoping for the fourth generation though.
He only has a B350, so I’d consider a 2700X as suggested by @dizmo.