So you can share a link to any group (as long as they are public) via web browser. You can grab a link from the invite function of a group you are an admin of via mobile. However you cannot grab a link via mobile for a group you are not an admin of. I find this very cumbersome when I’m trying to darned a quick invite (which happens fairly often). Don’t know if there’s an intentional reason for this or if this might be an oversight.