You can connect multiple accounts from the desktop client if that's what you mean... If you mean nextcloud to nextcloud there's also federation, but haven't really tried that as I've never needed it.
What client are you using? I have that capability on my Android client, Linux client, and windows client, and it works extremely well.
For example, from my machine, i can connect to my nextcloud, and also to some folders shared from my group's nextcloud.