Mouse issue while gaming

hi

Iam running on my 2010 i7 Imac.

When I play steam games (Palladins WofT) I have to press and hold left mouse button to aim. It is rly annoying. I had no isusses like that on OSSierra . I think it has something to do with mouse acereration. I cant rly go OSSierra is there a way to fix it for OS 10.10 ?