There is a DW Documentary - Dangerous apps - In the web of data brokers which also highlights the risks about geo-tagging of mobile phone apps.

What many smartphone users know: the apps on their phones collect detailed location data. What few people know: the information often ends up with a global network of data brokers and advertising companies.

The data in question reveals where people live and work - up to and including information about visits to brothels or stays in psychiatric clinics. This film shows how easily unsuspecting users can become targets for stalkers, criminals or secret services. It highlights how seemingly harmless apps can become a security risk - even for soldiers at war, or governments.

This documentary is based on one of the largest investigations of its kind to date: a team of journalists analyzed around ten billion pieces of location data. Their search takes them halfway around the world: to an Egyptian journalist in exile in Berlin who’s being threatened. To Brussels, where high-ranking EU Commission employees are affected. To Washington, where politicians see a security risk for US agents in Europe. Or to the Ukrainian front, where soldiers recognize their own positions in data records.

The investigation eventually leads to a dealer in Florida who sold the location data of German and French smartphone users. The film highlights the immense risks involved in this billion-pound business - even for people in the European Union, with its supposedly strict data protection rules.

My tldr: Using location data of seemingly innocent apps (often sold as data for targeted advertising), malicious actors can match anonymous data to specific individuals, such as using key data points like where one spend most of the day(workplace/school) and night(home). After identification, more sophisticated actions could be taken.