Please could you provide a link to an article, or other evidence, which supports this assertion?
EDIT:
I did wade through the linked article, which describes how Google’s Tag Manager could* possibly be used for tracking, but doesn’t provide any evidence that Google - or any other actor - actually does use it for the purpose of tracking individuals.
Google Tag Manager (GTM) extracts information primarily through its Data Layer, a structured JavaScript array on your website that acts as an intermediary between site events and tracking tools.
GTM extracts this data via a three-step process:
Data Push: Your website code pushes event information (e.g., purchases, form submissions, user IDs) into the Data Layer using JavaScript commands like dataLayer.push({key: value}).
Variable Creation: In the GTM interface, you create Data Layer Variables that explicitly tell GTM which specific keys from the Data Layer to monitor and retrieve.
Trigger and Tag Execution: Triggers listen for specific events pushed to the Data Layer; when a match occurs, GTM uses the defined variables to pass the extracted data to Tags, which then send it to analytics platforms like Google Analytics or advertising pixels.
This architecture ensures that GTM only accesses data you explicitly configure it to see, maintaining container efficiency while allowing third-party tools to receive consistent, structured information without direct code modification on your site.