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There is some fix it toolS to solve some common issues, windows troubleshooter tool is one of that kind. It fixes many issues by downloading pre-requisites of windows updates that are pending and then proceed to download original security patches or any other windows updates using the updates client application.
Use windows troubleshooter using a fix-it tool, and then try a manual install of updates.
There are some advanced methods to fix this 0x80070091 Windows update error using some commands and resetting your operating system to a healthy restoring point.