The following article explains how to hide a birth year in Personio. You can use this function to create annual birthday reminders without publicly sharing your employees' birth years.
Settings to Hide the Year of Birth
Under Settings > Employee information > Attributes, check the Restrictions checkbox in the "Birthday" attribute.
This hides the birth year from any employees with viewing rights for a colleague's profile:
In general, the year can be hidden for all attributes with the Date attribute type. You can find an overview of the attribute types here.