Short answer
HubSpot's KB: creating topic clusters in HubSpot does not affect SEO directly; it helps you structure content around main topics and subtopics. After your first topic, you can see a phrase's popularity and difficulty before creating it.
1. In HubSpot
The relevant screen in my demo portal.
2. Worth knowing
Use it as a planning tool and measure results in your search data.
3. Related
Search Console and SEO recommendations.