Saw your post on Reddit too. Reiterating here:
FYI: The User Manual for IK Product Manager states where the default location is for downloaded files and that you can change it (points you to the Settings section of the manual):
PLEASE NOTE: By default, the built-in download manager will download all software content in the following user folder:
/Documents/IK Multimedia/IK Product Manager
It is possible to change the download folder in the Settings panel (see dedicated chapter for Settings).
Also, I know on macOS the installer prompts you to send the file to the trash after the installation is complete. I don't have a Windows machine handy to double check the behavior there.
The manual installs with IK Product Manager and is also available on the IK web site.