In the main web page (meldmerge.org) there is a note for Windows installations which reads:
Note: The 3.20 Windows build uses a new build chain. If you experience issues, please use (SNIP)
I had problems on Windows 10 installating the .msi directly from Explorer, but was able to install Meld successfully by running the .msi from an elevated command prompt.
Suggest updating the message to something like:
Note: The 3.20 Windows build uses a new build chain. If you experience issues, please use (SNIP) or run the installation from an administrator command prompt.