This is a known issue on Azure devops. Now, we could only download the report, and open it with Visual Studio.
Azure devops only support the download link for .coverage files currently. The white page you see is a UI glitch. This scenario is only supposed to render a download link to the coverage file.
Besides, this issue has been submitted in this earlier suggestion ticket linked here:
support vstest .coverage "code coverage" build results tab
This feature request is On Roadmap, I believe it will be released soon, you can follow this thread to know its latest feedback.
In addition, we found a similar case and I have tested via the answer, set the code coverage tool to Cobertura, then I get the code coverage report in the Azure DevOps pipeline.