Use raw input on Minecraft 1.12.2 . Use /rescan if you reconnect your mouse.
https://github.com/seanld03/RawInputMod-1.12.2-gui-fix/releases
Fork of https://github.com/Fluorides/RawInputMod1.12.2, which is a fork of https://github.com/xCuri0/RawInputMod.