HTML Report Workaround

1. From the Jenkins home screen navigate to Manage Jenkins > Script Console and type in the following command:

 System.setProperty("hudson.model.DirectoryBrowserSupport.CSP", "")

2. Then press Run.
3. If you see the output as Result: below the Result header, then it has run successfully.
4. You'll need to Commit and Push again so that another build creates another HTML report before you can see one generated successfully.

Allure report

From the command line:

allure serve <xml or json file directory>