[RSS Feed/News] How to deny permission to close own threads?

[XenForo]

I have an user posting conflictive content and then, as OP, closing the thread to avoid being responded. I want to keep the thread open in order the others can post their own points of view, but this user keeps closing it every time I re-open it.

I can see options to limit or deny editing or deleting own posts, but not closing them.
Is there something I have missed in the ACP?

Thank you in advance for any help
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