Oh boy.
An agent needs full access permission on a group - without that, the agent cannot be the owner of a ticket. These permissions are explained here:
https://admin-docs.zammad.org/en/latest/manage/groups/access-levels.html
It’s just how Zammad’s erpmission system works.
Zammad, as of now, doesn’t support parallel browser tabs for the same user / instance. This has technical reasons. However, you have Zammads on board taskbar for multi tasking:
https://user-docs.zammad.org/en/latest/advanced/tabs.html
Generally you may want to consider to ‘cleanly’ divide agent and admin roles. Surely a admin only user sucks during configuration, however, saves you from accidential “oopsies” and is pretty much the norm by now from a security perspective.
Another reminder:
This is a community forum. Please try to be patient. If you require commercial grade support, there’s support contracts that give you this.