Personalized Difficulty and Topic Authority can be found in Topic Inventory and Reflect.
Personalized Difficulty is a metric that’s unique to your site and its contents. The value ranges from 1 to 100 — the higher the number the harder it is for you to rank. It’s calculated based on your site’s coverage of a topic, how well it performs (both currently and historically), and other factors.
Topic Authority can be considered as the difference between (Keyword) Difficulty, a generic metrics that applies to everyone, and Personalized Difficulty, which only applies to your site. The greater the difference between the two metrics, the bigger your authority.
Think of it as a probability indicator — the greater your authority, the more likely you are to succeed at optimizing an existing page or creating new content. It also reveals your competitive advantage as it means you have an easier time ranking for a topic than your competition.
Overlaying these personalized metrics on top of your standard quick wins (ranking on 2nd page of Google) approach can yield to more predictable success.