In certain scenarios where games or programs take control of the cursor, you may see a difference in cursor speed if the size of the display and some mouse settings are not the exact same between the host computer and the person joining.
To avoid this, ensure these things are the exact same between both systems: the screen resolution, scale of the interface (DPI), the mouse sensitivity setting in the operating system, and whether pointer precision/acceleration is enabled in the operating system. The person joining should also be using Parsec in fullscreen mode to ensure the size of the screen is the exact same between both of the computers.
On Windows, the mouse settings can be accessed by pressing Windows key + R, typing main.cpl and pressing Enter. The display settings can be accessed by right-clicking your desktop and selecting "Display settings".