@nutomic While testing things with lemmy, we verified that
To import a remote user we have lemmy.instance/u/nickname@gnusocial.instance. And that is working 
But importing a group with lemmy.instance/c/nickname@gnusocial.instance won’t. Looking at the logs we see that WebFinger is used to find groups via the acct: uri scheme. In GNU social we allow local users to have the same nickname as a local group (they are different namespaces). It has always been like this and we aren’t willing to introduce a breaking change. For us, and considering the RFC 7565 - The 'acct' URI Scheme, as @nedjo already elucidated, it only makes sense to support persons with the acct:.
Note that we don’t mind making groups and even different activitypub objects available in our webfinger endpoint, if that can be helpful, but that is as long as the resource is an URL or holds a new and more appropriate scheme (for groups that could, perhaps, be community:).
In GNU social, to fetch a remote group (or organisation), our users paste the Actor uri (or an alias) in the search box, and our ActivityPub plugin fetches it. We also have remote actions (OStatus connect), which is a button that opens a text input, allows you to write your home instance handle, and redirects to an endpoint with the URI of the group you were interested so that you can import it.
So the current state is:
- Importing Lemmy groups to GNU social via the usual GNU social UI/UX works.
- Importing a GNU social person via
lemmy.instance/u/nickname@gnusocial.instanceworks.
But I can’t find an alternative way to lemmy.instance/c/WebFingerHandle that would allow me to import a GNU social group. Is there anything in Lemmy’s UI that will allow me to paste the URI of the gnu social group and import it?