Could administrators have the ability to add apps from the Nextcloud app store to this when viewing the calendar and contacts links?
There is some extra steps required to use Nextcloud, and this is intentional as the ability to change settings from MiaB settings is considered a security risk.
So is it possible to add in the ability?
To do this you need admin access to NextCloud. Instructions for doing that can be found at the post below. As noted in that post, once you enable admin access, you’re on your own.