A lot of applications sell user data. Like menstrual cycle for Flo, seropositive status for Grindr. A lot of apps sell your location data.

Plus there is a very overlooked category of corporate software selling data, like payrolls. This can be used to target you better (eg can you afford that product). Another example is Salesforce selling consumer data to marketing departments: https://www.salesforce.com/products/marketing-cloud/data-sha...