The "anonymous" mode does not handle responses anonymously but confidentially (in the sense of GDPR privacy laws).
Even in anonymous mode, the authorship of the responses could be reconstructed in one of the following ways:

• As a teacher: by frequently recording the statistics of the query and comparing them with the access to the course of the students.
• For a user with access to the database: by reading the tables mdl_feedback_value and mdl_feedback_completed.

According to the GDPR an anonymous data collection must store the information in such a way that it cannot in any way identify persons.

What is expected? In the "anonymous feedback" mode the information must be stored preserving anonymity for all parties.

What is obtained? The anonymous mode only hides the personal information for teachers and students but keeps the relationship in the database. It is a "confidential" or "discreet" mode but not anonymous.

Proposed solution: Anonymity can be achieved by the following changes:

• adding a new "Truly anonymous" mode.
• The analysis of the responses is not shown until the feedback is completed.
• The records in mdl_feedback_values are merged with the records in mdl_feedback_completed by randomising the order and the pseudo-FK mdl_feedback_value.completed
• The analyses are not shown if there are less than 3 answers.

A proposed solution is at https://github.com/juacas/moodle/tree/feature/feedbackanoymous_39

This patch has been in production for 3 years to full satisfaction and without problems.

I think this is an easy to implement and useful improvement.