bbPress.org

There is a plugin called “my views” that has many view options:

https://bbpress.org/plugins/topic/my-views/

Or there was “Posts since last visit”:

https://bbpress.org/plugins/topic/posts-since-last-visit/#post-65

But that’s pretty old, not sure if it still works.

Or there was “Indicate new posts”:

https://bbpress.org/plugins/topic/indicate-new-posts/

Both required “Simple online list”:

https://bbpress.org/plugins/topic/simple-onlinelist/