Unfortunately, at this moment, the only way to find which apps are using which extension, is through scanning the app for object ids => get each object's properties => check if extension exists in QRS etc...
But there is an extension created by swr for that: GitHub - stefanwalther/sense-extension-governance: Analyze usage of Qlik Sense visualization extensions across your enti…
I hope this helps
OK, well after digging further, I don't think this extension will work for us. It requires that all apps are closed in order to run, and that would be very difficult to accomplish in a large organization with many thousands of apps.
Do you know of any way of doing this without having all apps closed?