I've been using Designer 2021.1 and 2021.2 (and some of the 2020.* versions) on a Windows machine without issues for almost a year. We've recently got an Alteryx Server up and running, but when I tried publishing some workflows, I got errors indicating that my version of Designer was later than the Alteryx Server version, and the workflows would not run at all on Server.
I uninstalled my Designer without issues, then installed the 2020.4 version. The installation worked fine right until the end where I got the following error:

After closing this error, the installer window reported that the installation had worked successfully, but I cannot launch Designer at all. The Designer .exe file is in the C:\Program Files\Alteryx\bin directory, but running it does nothing.
I uninstalled the 2020.4 version without issues and re-installed the 2021.1 version, but that produced the same error and running the executable does not launch the application.
Is there anything else I should try doing to get Designer to work? I've never had this issue when upgrading versions, only now when I tried to install an earlier version.