I unable to create a new topic in the Documentation topic category

Specifically in Documentation - The Document Foundation Community.

I was able to a few weeks back but now the option is greyed out, what happened?

That category is read-only and has been since it was created. Use one of its subcategories instead such as #documentation:general or #documentation:localhelp. AFAICT your previous topics were posted to these two.

Got it, thanks for the information!