Building a Cohort Retention Report for Workshop Engagement Tracking

Hi all, I am stumped and wonder if anyone might have some insights to share. We want to create a retention report for a set of cohorts. Each of these cohorts joined a workshop on a different day. We want to be able to track engagement retention after the completion of the work shops and show all of the cohorts on one data viz if possible in a week by week (week 0, week 1, week2, etc) basis so we can see which workshops has the largest impact on retention. I have asked Kapa, and Chat gpt and I am stuck. IS this even possible? I got as far as adding a custom user property to profiles in the cohorts to use the workshop dates, but I wasn’t able to do much after that.