The Dashboard app is unsupported since the first and only release more than six months ago. There are some issues and the app does not work properly with Nextcloud 13, too.
Dashboard is not listed on the list of supported apps, it seems that the app has been abandoned.
I’m interested in that, too.
I was looking forward to using this app, but it didn’t work in NC12 nor does it in NC13. The only (correct) information it provides, is the Quota.
Would be nice, if the app will be improved to actually work.