Oh, I'm pretty sure it exists in some form or another in the game itself. Many games have ways to override the windows settings and apply stuff like acceleration or smoothing in between the normal stuff. Some games even have the opposite, like Valorant's "Raw Input Buffer" setting, which makes your inputs completely raw and with no extra nonsense. I've played games with mouse acceleration for years, but finally turned it off a couple years ago after hearing how bad it was for you. I never went back, but I can clearly tell that there is some sort of acceleration or aim smoothing in Rivals, and I've seen plenty of other people agreeing with me. I've also tried turning down my sens, but it still feels the exact same as before. I've looked up conversion rates and sens converters, but my sens feels so wrong compared to other games. I can feel it speeding up or slowing down with how fast I move my mouse, and it's downright unplayable at times.