You may get "update is not applicable" for a couple of reasons. Either the prerequisite SSU has not been installed
https://support.microsoft.com/en-us/topic/servicing-stack-update-for-windows-10-version-1809-august-11-2020-8556774b-6173-605d-c566-eb9b9eef76e1
or a newer cumulative update has been installed. You can check the results of
(Get-HotFix | Sort-Object -Property InstalledOn)
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