Game is without Vsync?

With VSync various computer games like Rainbow Six Siege or Fortnite run relatively well but not at all although I have more fps. Some 200 fps more.

Play on a 144Hz monitor

Have you ever thought that the more warm your hardware gets, the more it has to work? For the CPU and graphics card, this means that they clock down from a certain temperature. This is how you get these laggs.

More FPS than the screen can process can also lead to stutters, since the monitor does not know which frames to skip and this can lead to jumps.