The screenshot isn't coming through. Normal conditions can be add be added via the + button on the right side. If you are referring to nested conditions, search the manual for the chapter on those.
It seems you modified the nested conditions so that they are no longer nested. See how the "Extension" popup is now flush with the "If any" above it? You need to drag the conditions back so that they are indented. For comparison, see how "Date added" is indented in related to the "If all" above it.
This works - many thanks! But what if I have more than 5 extensions? It would seem that a list matching (or something like regex) would be quite useful