There are no major downsides. SonarQube v10.6 simply has some new features that you’ll get when you upgrade (specifically no longer having to maintain the version of Java on your build agents to match SonarQube’s requirements).
I will flag this for attention to see if we are firmly set on this log level, or if we can add some more messages (Version of SonarQube < 10.6 detected, proceeding as normal… something like that)