Shopify app primers / materials

Does anyone have materials or primers on the Shopify app ecosystem?

I'm reviewing a Shopify app opportunity and would like to hear any insights / experiences Searchfunders have had with the space, and understand averages for KPIs (primarily focused on churn and retention, keeping in mind this will vary across types of apps), what makes an app sticky and unique, and whether there's significant platform risk / risk of Shopify making apps obsolete by building features in house.

Appreciate any guidance.