The New Topic/Open Draft button is greyed out when on certain category pages. I usually bookmark the IDN category but was not able to create a different post from that page.
Great catch! This is actually by design, so nobody accidentally creates a new topic in the general IDN category, so that they will explicitly create a topic in in either ‘Discussion and Questions’ or ‘Show and Tell’.
I can also enable a flag that will give you a header to explain why, but this is the reason. I’ll see if it’s also possible to put a hover text on the disabled button explaining that as well.