Anonymized tracking - How does it work technically?

Hello,
as explained in this help article (https://help.brevo.com/hc/en-us/articles/11643306229906-Can-I-anonymize-the-tracking-of-opens-and-clicks-for-my-emails), it is possible to anonymize the tracking of clicks and openings.

It is a problem in terms of data protection if the data is initially collected individually and only anonymized in a further step. This is because, in fact, individual data processing still takes place.

My question is therefore, when and how exactly is anonymization technically carried out? Is the data first collected individually and then subsequently anonymized or is no individual data collected at all?

Thanks in advance
Jonas