This has been going on for MANY years/versions of Illustrator and I've seen many posts here about the issue but it's yet to be resolved or have any work arounds.

All you have to do to replicate the bug is to hit alt (don't even need to hold it) and assuming you're on a high refresh rate monitor you will instantly feel input lag and see the cursor moving at what appears to be 30fps or less, until you left click with mouse, then it will go back to normal. When you hit ALT there should be no difference in the rendering of the mouse cursor. It should feel and look just as smooth as before you hit ALT.

While this isn't a program breaking bug it's still annoying nonetheless. When you're used to moving the mouse at a certain speed and you hit alt to duplicate or whatever you want to do the mouse instantly feels off/slow and it really breaks down the smoothness of the program to me since ALT is a very critical hotkey.

Please work on fixing this next update.

This happens on newest version 28 and has happened on every version of illustrator as far back as I can remember over 8 years. Win 11 64 bit fully updated but again happened on Win 10 64 bit also. This is NOT an operating system specific issue. This is a bug within the Adobe Illustrator engine.