Despite the v1.0.0.2 hotfix, the id Tech 5 engine remains temperamental on some modern PCs. Common complaints include:

If you use GOG’s official client, updates are typically handled automatically. If your game has not updated, use the following steps:

Situations where NPCs fail to interact, preventing the mission from continuing. How to Get the v1002hotfixgog Patch

The id Tech 5 engine struggles with Screen Space Reflections (SSR) on modern hardware architectures. Turn this setting down or off in the advanced video options menu to instantly boost your frame rate by 15–20 FPS. 2. Force Triple Buffering

If GOG Galaxy handles updates automatically, enable automatic updates in the game's settings and use "Check for updates" in the game's context menu.