Are they able to pin/unpin the topic for everyone or for themselves?
When you pin a topic, you use the wrench menu
and select where the topic should be pinned
That menu should be only visible for TL4 users and staff.
But as the second line says, when a topic is pinned, every user can unpin it for themselves using the dropdown at the bottom of the topic or by clicking the pin icon next to the title. They can also configure to unpin topics automatically after reading them, which is enabled by default if you didn’t change the default for your community (default topics automatic unpin)
