I have used the -Dsonar.exclusions parameter in Sonar scanner to exclude certain files, I think that gets excluded from the coverage, but not from the duplication check… the version we are using is 8.3, I have also tried the GUI option to ignore duplicate files at https://docs.sonarqube.org/latest/project-administration/narrowing-the-focus/
sonar.exclusions parameter entirely excludes the relevant files from analysis. Issues, coverage, duplications, …
The docs you cite do include directions on setting duplication exclusions. You’ll find the setting in the UI:
You can prevent some files from being taken into account for code coverage by unit tests.
To do so, go to Project Settings > General Settings > Analysis Scope > Code Coverage and set the Coverage Exclusions property. See the Patterns section for more details on the syntax.