It seems to be an old bug, that should be fixed by using jre 9+:
I confirm that I still have the problem with Sonar Version 9.9.4 (build 87374) (Java 17.0.11) and a sonar-project.properties encoded with utf-8 (not latin-1 / ISO-8859-1):
sonar-project.properties
sonar.projectName="Test accentué É 😁" => "Test accentué à ð" sonar.projectDescription="utf-8 é`èçàÉÈÀàùöï😀🍟" => "utf-8 é`èçà ÃÃÃà ùöïðð"