The title says it already: I'm trying to create a block that shows the full first post of the latest created topic of one forum.

I want to use that for official site news.

Anyone got an idea how to achieve that?

Use Block Manager - Forums - Post Feed

Insert this widget into a field where he wants.

Use editing and only select one post

That doesn't work for me.

It seems to show the last post in the topic, not the first one.
So if anyone comments on that post, it shows the comment.

Then try the Topic Feed 

But the topic feed only shows the topic, not the full post, does it?