Can anyone shed light on what might have happened please?
It appears that Microsoft is pulling some shenanigans with their Microsoft Edge and Windows Defender products. It looks like some corporate maneuvers going on, where Microsoft is trying to
push people to their
Microsoft Store. Often, if you attempt to download something outside of their store, even if well known open-source projects, you can get warnings from the Edge browser (SmartScreen) or Defender.
The only thing that can be done is to report the false-positives to Microsoft.
With Windows Defender, you can
send a report to Microsoft directly. They will do an analysis and give you the results within 24 hours.
https://www.microsoft.com/en-us/wdsi/filesubmission/(Submit a file for malware analysis)With Microsoft Edge, it's a little bit trickier. When it stops the download from being saved to the hard drive and indicates red, there is an option to give feedback on if you believe the download is safe. But, it doesn't always show up, and sometime it just allows you to save the file to you hard drive with no other options. Thus, it is probably a good idea to then submit the file to Microsoft's website for malware analysis so that you can confirm it is safe and remove the false-positive indications.
Microsoft Edge is using SmartScreen, which is linked to Windows Defender, but has additional functionality. A person has the option to turn it off, but that will kind of only help you, not other people who want to download your file. Microsoft states that to help with the reputation of your file (to prevent SmartScreen interference), it should be digitally signed.
Here is quasi helpful advice that Microsoft gives on the subject.
https://feedback.smartscreen.microsoft.com/smartscreenfaq.aspx(Microsoft Defender SmartScreen Frequently Asked Questions)