Is there any documentation about adding buttons via hooks?

Sorry, for the late response. 

The widget updates all of the buttons to point to /user/ except for the "favored" button. That button directs to the wpForo profile page. There isn't a place to change the link or add/remove buttons.

This will be fixed in the next update of the wpForo plugin.

Regarding the other request, it can be implemented using hooks. Currently, there is no built-in solution for adding buttons.

• Ultimate forum links are set to /user/
• wpForo links are set to /member/

The widget updates all of the buttons to point to /user/ except for the "favored" button. That button directs to the wpForo profile page. There isn't a place to change the link or add/remove buttons.

I cleared cache and flushed Permalinks.

What is the best solution for this, or where can it be edited in the code, function, etc?

Slightly off-topic, the same thing happens with messages. Better Messages support isn't offered by wpForo, but it is integrated with UM on the UM profile page. Understandably, there is only a message button when the wpForo private message plugin is active, but it doesn't know to point to the UM messages tab. Also understandable, but it would be better if there was a way to easily edit button links or add custom buttons. Especially since the wpForo notifications function doesn't really integrate well with anything else outside of wpForo.