“Leith says the DSID advertising cookie is created shortly after the user logs into their Google account – part of the Android startup process – with a tracking file linked to that account placed into the Google Play Service’s app data folder.”
Android sets an advertising cookie as soon as you log in, before you open an app or consent to anything. Another identifier survives logout, and only a factory reset removes it. Google’s own code treats it as personal data under GDPR. Google disputes the analysis and names no error.