To answer your question, no, there's no specific section dedicated to DeFi on the forum, but it can fit into a variety of boards in the altcoins section depending on the context of the topic. You can make a thread there is you want to.
DeFi has attracted quite a number of discussions and could have a child board, this is up to the admins to decide, for now you can use the forum search option to discover posts and replies related to it.