In a smaller and less active forum, it’s easy for many of the most recently bumped threads all to show the same user avatar, because one of the users has just responded to several threads. This gives the impression of dominating the space.
Is it possible to show instead - as a site setting - the thread author, or a sample of the contributors?
I want my small and inactive forum to look attractive to newcomers - I choose the Categories view because it gives an overview of the various things we discuss. But it has this disadvantage.
This does exactly what you want, but also alter the topics list like /latest layouts.
It works by overriding an existing template.
If you want to change only the /categories layout, you can follow these instructions:
Note that templates sometimes change in Discourse, so the new code may need adjustments from time to time (it could also go for years without any modification needed).
I got all of this info by searching #support display topic author avatar
I got all of this info by searching 
