Hi Grace,
Thank you for posting here.
As far as I know, stack updates may not be uninstalled directly. In the update detail information of some stack updates, there is a clear notice: "After you install this servicing stack update, you can't uninstall it to revert to an earlier version
of servicing stack update." If you force Uninstalling updates quoted as “permanent” bears the risk, that further updates can’t be installed due to serious errors like STATUS_SXS_COMPONENT_STORE_CORRUPT.
I verified the Permanence property of KB4490628, we can't uninstall some updates because they are marked as permanent in their manifest file.

Hope the above can help you.
Regards,
Yic
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