The forum […] is used by some community members as something supplementary to Gitter chat.
Github and Gitter is where it is happening, and then all across the web, including here by some of us. For me that is good to know, as I am used to these kinds of forums to be central to a community, but there is not really a community, only a forum (solidproject.org also indicates that with a single ‘Forum’ link and ‘Integrate Solid’ leading to a business intake process).
I did spend a lot of time here suggesting improvements to Solid positioning, organization and community structure, but that may be a bit of a waste of time 
However, all this should be more clearly communicated to all current and future solid members.