Unable to create topic - new users can't put links in posts

I’m trying to post a new FreeRTOS related topic, but it says, “An error occurred: Sorry, new users can’t put links in posts.”

I don’t have any URIs in my post, but it seems to think there is a link. How does it know? Is there a regex to avoid?

I think I figured this out - it’s the square brackets that are considered a markdown link.