Originally posted by mikou:

Since 1st level I can't turn off the flashlight, is it even toggleable? Restarting the game didn't help.

This is not a bug, but a feature. Initially, it was intended that the flashlight would turn on automatically in dark areas of the levels and turn off in light areas. But I received a lot of reports that the lighting in the game was quite dark, so I decided to give players the opportunity to turn on the flashlight wherever they want.

if you are running 1.09 you can go to controls and set flashlight key which is empty by default and set it to your preferred key mine is F.