Board Thread:Support Requests - Getting Started/@comment-32734993-20191230113027/@comment-37425278-20191230113322

It's not a feature, it's a script.

The one that you're referring to is LockForums in the dev Wiki.

The current configuration of the script in the Wiki's JS page: window.LockForums = { lockMessageWalls: true, expiryDays: 90 };