Topic on Talk:Atomic Heart
Both User:Yobson and I have tested the game over on the Discord and failed to note any presence of actual mouse acceleration in the game.
It would seem that some users are mistaking the abnormally high mouse sensitivity for mouse acceleration.
The solution is to turn down the mouse sensitivity by like a ton. On my 250 Hz 1600 DPI mouse, I had to turn it down to 15% to get anything close to regular movement, and I imagine users with higher mouse polling rates needs to turn it down even further -- probably using both the X and Y axis sensitivity sliders on top of the general mouse sensitivity slider the game has.