I would like to see this as well. It’s very helpful on desktop to see both latest posts and all categories. This provides an overview of the forum (for new visitors), at the same time as displaying what’s new (for returning users).
However, on mobile, seeing latest topics is more engaging than seeing the same categories every time. This is particularly true in my use case because I have my categories in a static order reflecting their general importance; thus new posts don’t rise to the top on mobile unless they are in the top category.