insert pictures for category

Can you explain further – where do you want pictures – you refer to a font field

No no, it’s my idea, to insert for each Category, pictures.
Item 6. is the place, were I would insert this pictures. (Before the categories)

do you mean a thumbnail before the text?

yes something that…

ok,for categories, put this is your functions file

function add_thumbnail () {
	$pic='<img src="https://blog.monitor.us/wp-content/uploads/2012/04/html2.png" height="25" width="25" alt="">' ;
	echo $pic;
	}	

add_action( 'bbp_theme_before_forum_title', 'add_thumbnail' );

see

https://codex.bbpress.org/functions-files-and-child-themes-explained/

Forums is doable but would require coding beyond the ‘free’.

this is for all categories or only one?
And how can I make each category its own thumbnail?

this is for all categories or only one?

all categories and top forums

And how can I make each category its own thumbnail?

Lots of coding !

Sorry not a simple solution:-(

you could try posting in

https://bbpress.org/forums/

but many of the answers are mine !