It downloads, but when it tries to install, it just says update failed. Details icon provides no info.
How are you trying to update the Quicken version? From within Quicken?
If so, you might want to try downloading and installing the Manual Patch Update file from https://www.quicken.com/support/update-and-patch-20182019-release-quicken-windows-subscription-product/ .
Just tried the Manual Patch Update. If fails to install also. Doesn't give any reason.