Spring Tool Suite not picking up the plugin

Using latest version (3.9.5.RELEASE)
Build Id: 201807031753
Platform: Eclipse Photon (4.8.0)

I copy the google-java-format-eclipse-plugin_1.6.0.jar file into dropins directory, restart STS, but still don't see the google-java-format option under Preferences -> Java -> Code Style -> Formatter.

When I use the previous version:
Version: 3.9.4.RELEASE
Build Id: 201804120921
Platform: Eclipse Oxygen.3a (4.7.3a)

And follow the same install, I do see the option.

Even when I took the 3.9.4 STS and updated it to 3.9.5 (updates parts of it but not the Eclipse platform):
Version: 3.9.5.RELEASE
Build Id: 201807031734
Platform: Eclipse Oxygen.3a (4.7.3a)

And follow the same install, I still do see the option.

Is the plugin supported by Eclipse Photon 4.8.0? Or is there any way to troubleshoot?