Stuttering in fullscreen games

Ever since upgrading to High Sierra (10.13), fullscreen games such as Team Fortress 2, Counter-Strike: Global Offensive and Half-Life 2 have been suffering from stuttering issues, also causing FPS drops (around 10) and input lag, rendering the games practically unplayable. Non-Steam fullscreen games like Xonotic are also affected. Changing to windowed mode does not solve this problem.

However, Windows games like Deus Ex run normally with Wine.

For Team Fortress 2 (which shares game engine with CS:GO and HL2):

- Activity Monitor shows no anomalous process activity.

- Console displays no log entry pertinent to game process "hl2_osx".

- Giving focus to the game does not bring forward the game window.