I doubt many people will play this game these days, but the game engine has a bug where enemies don't take damage if the FPS is too high.
I don' remember which method I used, but you can force vsync with either the AMD or Nvidia control panel, or set a framerate limit with either one. As both the AMD control panel, and Nvidia control panel have a way to limit the framerate if you have a recent card.
RivaTuner Statistic Server should also work.
https://blurbusters.com/gsync/gsync101- ... ettings/12