The following activities would make a prospect active in Marketing Cloud Account Engagement:

Submitting a Marketing Cloud Account Engagement form, which indicates the prospect's interest and consent to receive communications from the company.

Clicking on a custom redirect, which tracks the prospect's engagement with external links or downloadable content.

Visiting a Marketing Cloud Account Engagement-tracked page, which captures the prospect's browsing behavior and page views on the company's website. Reference: [Marketing Cloud Account Engagement Prospect Activities]