Our security researchers were unable to find a way to exploit the Log4J vulnerabilities in recent versions of SonarQube (earlier ones not tested). We nonetheless issued patches to quiet fears and alleviate confusion. If you have concerns, you should definitely upgrade to the latest patch version: 8.9.6.
The Upgrade Guide should help. The only difference from a standard upgrade, is that since it’s just a patch version, there shouldn’t be any schema changes to make. So it should go really quickly.