"Accounts" Address Book is not used internally for other Apps

Describe the bug

All our Nextcloud System Users are automatically part of the "Accounts" Address Book, however contacts in this Address Book seem to be ignored by Nextcloud Apps like Mail or Calendar.

Steps to reproduce

1. Go to Nextcloud Mail
2. Click "New message"
3. In the "To Recipient" start typing the name of one of your colleague that also has an account on the Nextcloud instance and that you have never sent an email before
4. It will not find that colleague and auto fill the recipient in the To field for you however you can find the contact in the Contacts list in the Contacts App

Another example:

1. Your colleague has filled in his birthday date and allowed to share it with other members of the Nextcloud instance
2. His birthday will never appear in the Calendar app

This goes for all contacts that are stored in the "Accounts" address book

Expected behavior

All contacts in the "Accounts" Address Book should be retrievable in Mail & Calendar and all other Nextcloud Apps

Actual behavior

Contacts that are stored in the "Accounts" address book are ignored by other Nextcloud Apps, like Mail & Calendar

Contact version

7.3.0

Operating system

Debian

PHP engine version

None

Web server

None

Database

None

Additional info

I am not sure if this is a Contacts app bug or if the maintainers of Mail & Calendar have not implemented the "Accounts" Address book in their code...
Anyway I would appreciate you are having a look at it and work it out with the other App Teams

Reproduce the missing colleague lookup in Nextcloud Mail and the missing shared birthday in Calendar, then compare both with the Contacts app's Accounts address book. Trace whether the Accounts address book is exposed to other apps or whether Mail and Calendar omit it; done means these contacts are retrievable in both examples.