@m.schmidt, if you replace any user identifiers in those user properties by account IDs, then you will not be storing any personal data. The project ID is an Atlassian entity identifier, and the personal message is user-generated content. Neither is considered personal data.
As long as you store user keys or usernames or other personal data in user properties, you will be required to select “Yes” in the Marketplace selector and report on these user accounts. Once you complete the migration to account ID, you can select “No”.