The GDPR and the Convention 108 are two important data protection instruments that aim to protect the rights and freedoms of individuals with regard to their personal data. They both have some similarities and some differences, but one common feature is that they both require notification of processing activities to a supervisory authority.
A supervisory authority is an independent public body that monitors and enforces compliance with data protection laws. In the EU, there are 47 national data protection authorities (DPAs) that have the power to impose administrative fines, issue guidelines, conduct investigations, and cooperate with other authorities1. In the Council of Europe, there are 54 parties to the Convention 108 that have established their own supervisory authorities or have agreed to be supervised by an external authority2.
Notification of processing activities is a requirement for any controller or processor of personal data that falls under the scope of the GDPR or the Convention 108. A controller is a natural or legal person who determines the purposes and means of the processing of personal data3. A processor is a natural or legal person who processes personal data on behalf of a controller3. Notification means informing the supervisory authority about certain aspects of the processing, such as:
The identity and contact details of the controller and processor
The categories and sources of personal data
The purposes and legal basis for processing
The recipients or categories of recipients of personal data
The retention period or criteria for determining it
The existence of any automated decision-making or profiling
The rights of data subjects and how they can exercise them
Notification can be done in various ways, such as:
Submitting a written notification form
Publishing a notice on a website or other platform
Sending an email or other electronic message
Using an online system or portal
Notification should be done as soon as possible after becoming aware of any relevant information about the processing. It should also be updated whenever there are significant changes in relation to the processing4.
Therefore, both the GDPR and the Convention 108 require notification of processing activities to a supervisory authority. This is one way to ensure transparency, accountability, and compliance with data protection laws.

Explanation/Reference: https://www.itproportal.com/features/heading-off-the-spectre-of-gdpr-compliance-with-secure-byod/

Reference https://dataprivacymanager.net/pseudonymization-according-to-the-gdpr/