@damsonwhufndthis saw this on reddit, maybe this will help you. this is the short explaination.
"There are two types of aim assist present in apex, aim assist slowdown and aim assist rotation. Rotational aim assist does some degree of tracking for you and makes your crosshair or reticle follow a player without your input within a certain portion of your field of view. Aim assist slowdown is basically just sticky aim that slows down over a target to allow for better precision.
source:
https://www.reddit.com/r/CompetitiveApex/comments/lat63y/the_problem_with_aim_assist/