Not true, looking at systemd main branch shows the field still exists. Here’s the state as of posting this comment:
github.com/systemd/systemd/blob/…/homectl.xml#L37…
Also ping @[email protected] fyi

This reverts commit acb6624, reversing changes made to ba1caf0. Revert "userdb: add birthDate field to JSON user records (#40954)" After extensive community discussion, legal review and c...
Status: Closed
That means it wasn’t accepted, see also the last comment before closing:
It’s an optional field in the userdb JSON object. It’s not a policy engine, not an API for apps. We just define the field, so that it’s standardized iff people want to store the date there, but it’s entirely optional.
Hence, please move your discussion elsewhere, you are misunderstanding what systemd does here. It enforces zero policy, it leaves that up for other parts of the system.
And sorry, I am really not interested in these discussions here. it’s not the right place for this, and please don’t bring it here. Thank you.