Hi,
How did you install it? Through Windows Update agent in Settings or download update package manually?
Make sure you have installed the latest SSU KB4565912 before installed this update package KB4565511.
Make sure you chose correct system structure if you download manually.
As the issue could be caused as this update package exists on your computer or existing system version upper than this package.
So, please run command line "wmic qfe" as administrator to check installed package on your computer, then upload command screen capture here.
Run "winver" in Run box to check exact system build and feedback the build number to us.
For detail description about error "The update is not applicable to your computer", please refer to the following official article and check "the update is not applicable to your computer" part.
Windows Update troubleshootingwindows-update-troubleshooting
Bests,