i’ll tell you: you’re not supposed to play it with a mouse, use a xbox and your golden. 
In all seriousness, negative mouse acceleration has been an issue since one of the earliest updates in FS2020, introduced in an effort to make the game more comfortable for controller users. This clearly highlights the developers’ priorities.
Beyond the mouse bug described here, another issue is negative acceleration. Essentially, if your mouse movement falls below a certain speed, the game fails to register it properly, resulting in laggy, stuttering view movement, as demonstrated in this video. Under normal circumstances, mouse input should always provide smooth and consistent movement. However, in the simulator, this is not the case. At the 1-minute mark, the video switches to head tracking, which maintains the same steady motion—yet unlike mouse input, it translates correctly within the game.
also @hobanagerik wrote about it in 2021:
this one got 55votes, was closed and never fixed: