Hi Rob,
As far as I know, the .coverage file is stored with XML by default. Please right-click your .coverage file to choose open with -> Notepad. Then it will shown with XML content in that file.
And you also can change the .coverage extension to .xml directly, which will also can convert it to XML file directly. I have changed the .coverage extension to .xml and then import this xml file to Visual Studio to check the code coverage result, it is
successful.

Before changing the extension for your .coverage file, please take a backup for this file.
Best Regards,
Weiwei