Can I restrict the recipients of an "invite to comment" for my diagrams? So that just people from one organization can be invited and not any random person.
No, normally you can invite whomever you want. As a workaround you can set the IP address filter. Then only people with a special IP or within an IP range can use this link. All others coming from a different IP will not be able to comment. You will find more information about the IP address filter here: https://docs.signavio.com/userguide/editor/en/workspace_admin/manage_users_access/managing_security_settings.html?