What analytics to collect to determine the interest of the reader?

Question

Marketing

Primarily interested in content projects, blogs, news, etc. How to determine that a person is interested in the content provided?
What actions, events to track?

Answer 1

- the number of open pages per session
- the time spent on the site before closing the page
- returning to the site within a certain time

Answer 2

Time spent on page
Scroll to the bottom
Clicks on related content

Answer 3

heatmap is also cool, but for analysis it becomes a big data even with a small number