I attempted to use Check for updates > Check now in Rhino 8 WIP to download the Beta version released 12 Sept 2023.
The file downloads 100% but instead of converting the “Unconfirmed” download to the .exe file Windows 11 shows a message that the file is not commonly downloaded and deletes it.
I was able to successfully download and install the update by downloading from the Web page. When I clicked to install the .exe file Windows 11 showed a message that the file might be unsafe. I clicked on “show more” and then clicked on “run” and the new Beta was installed.