The small patcher unlocks all resolutions in the game and removes black bars.
Make sure to follow both steps and patch both files covered by the tool.
The game is likely to reset to 1920x1080 and windowed at the start of each chapter, which is a known issue with the game itself. In that event, simply go to the options and set them back.
Tested the latest GOG version at 2560x1080.
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