Hi, we have a usecase, where we use the ticket system with a bunch of agencies. Those agencies shall have access to tickets assigned to them but sometimes it can also happen, that they need to work together with other "departments" and as we do not want to clone all comments all time to tasks, we work witth tickets and comments, only.

We set the access level to private. Cite from documentation:

Simplified summarized, we set up a hierarchy of roles. Lets say topmost role is Admin, then we have below Marketing and below that we have Agency1 and Agency2.

Now, if I assign a ticket to Agency1, it can only be viewed and worked on with users inside Agency1. If I assign it to Marketing, it cannot be viewed by Agency1/2, only by Marketing and Admin. So far, it works.

However, the concept to bind access to ownershop only is a problem in RBAC. We now faced the problem, that we have briefing tickets with content for a completely different team under Admin, lets call it "Design". It is a sibling to Marketing. Sometimes if Design owns a ticket, it is required that one of the workers having Agency1 as a role need to do some work there and should see the ticket, all comments and be able to support. We cannot give him role Design as that user shall only see that single ticket. We cannot assign an additional owner so he and his colleagues might see the ticket.

Is there any way how we can either add several owners (which makes no sense conceptwise) or grant access for single additional roles or users? If not from Zoho, then any plugin?

If the described request is unclear, just check any other RBAC, e.g. AC in any Linux or Windows OS. There is one owner but you can add access to different entities.