IG is also invite only now, so if you are not approved you cannot release any game at all anyway. So the plugin is not used so much any longer..
It is indeed a rarely used export option since Meta changed Instant Games to be invite only. It is now one of the least used export options in Construct.
We developed the Instant Games plugin on the understanding it was a platform open to anyone and so potentially attractive to many Construct users. Then Meta went and changed the rules and it is far more exclusive now and harder to justify having in Construct. So I don't think we will do any more work on the Instant Games plugin. Third party addons can still extend it or you can use JS coding directly in Construct to access the API yourself.