This is a bit of a mystery.
In one category only, with Decaf theme, the green edit button does not appear, instead I get this:
It looks like Ajax is not working maybe?
I have shifted courses out of the category into other categories and they now are OK.
I cannot find anything at category level that is a setting I have changed. I cannot find any odd code that may break something like in a category description.
It has been like this for over a year through several versions of decaf and moodle 4.3/4.4