Usage patterns
〈事〉をトピックにするto make something the topic (of discussion)
Let's make environmental issues today's topic.
〈事〉というトピックについて話すto talk about the topic of ~
We talked about the topic of the future of AI.
トピックが変わるfor the topic to change
The topic changed partway through the meeting.
トピックを選ぶto choose a topic
It took time to choose a topic for the presentation.