Accept recordings from Windows 10 default Voice Recorder
It produces m4a
The default browser on W10 is Edge and Silverlight does not work on it.
As Win 10 is presumably the most common OS on new computers it would be good not to have to hunt around for software.
For anyone still reading this, you can use a converter. For example, VideoLAN, a free software, has a converter function from M4A to other formats such as OGG.