You are right.
I don’t remember ever setting a theme by default, but maybe I did and forgot about it.
I’d like to temporarily disable themes by default, so that our forum is usable while we figure out what is wrong with themes. How can I do that, if I can only access the admin pages with themes disabled? In safe mode, all themes are already disabled, and enabling and then re-disabling them seems to have no effect.
There are three themes available (see below). None of them is enabled by default.
Also, in safe mode there is no Content-Security-Policy error.