[2021] Mouse input-lag

DXDIAG is a program you run from a command prompt or the Windows start menu 'run' dialog box (or 'search programs' in Windows 7 or later). After running it will open a window and start collecting info with a progress bar in the lower-left corner. When it completes click the 'save all information' button and save it to a file then attach that file here.

Please attach your Documents/Paradox/CK3/pdx_settings.txt .
From your Documents/Paradox/CK3/logs/ folder, attach system.log .  

You may as well, but by now we're pretty sure this is not a game problem.

You can test your theory that it was caused by the latest game patch, by reverting to an earlier one in the Steam Betas tab for the game. If a version that used to not have this problem for you now does, the cause is outside the game.