An instance is a collection of sites. Each of those sites needs to have a place to have its meta discussions (scope, why was this question handled this way, should we merge these tags, etc). An instance probably needs a place to have instance-wide meta stuff, since each instance is free to set its own policies and stuff.
Then there’s the Codidact project itself, which needs a place to discuss changes to the platform and stuff like we’re discussing here on this forum. Presumably bugs and well-formed, complete feature requests go to GitHub bug-tracking, but there also needs to be a place to work stuff out and discuss stuff. I don’t know whether that’s this forum, something on Github, or what.
The Codidact platform is different from Codidact instances, though we expect this team to stand up an instance on top of the platform.