If you are experiencing stuttering with mouse movement in Halo: MCC, there are a few possible solutions to try:
Update your drivers: The stuttering may be caused by DPC spiking drivers, and in both cases for the poster, it was caused by ethernet drivers. Try updating your drivers to see if this resolves the issue.
Disable fullscreen optimizations: To do this, right-click on the game's .exe file, select Properties, go to the Compatibility tab, and check the box that says "Disable fullscreen optimizations."
Disable Game Mode: disabling Game Mode in Windows 10. To do this, go to Settings > Gaming > Game Mode and toggle the switch to "Off."
Verify game files: Verify the game files to ensure that the installation is not corrupted. To do this, go to the game's properties in your Steam library, select the Local Files tab, and click "Verify integrity of game files."
Hope this helps.
PC Hardware Specialist