Introducing nested replies

On my forum, I don’t see a “view as flat” option like in the example screenshot.  For me, I need flat as the global default, with nested being an optional view that users can use when they want to, with flat always being readily available.  As long as it’s a “view as nested” button which people can toggle back off, this would be great. A per-user setting to switch to nested as the default would also be great as long as they can switch individual topics or all topics back to flat at will.  Withou...