Each birthday and work anniversary can be celebrated publicly, privately, or not at all, and the default is Celebrate Publicly (Recommended). Every member can choose their own setting in Account Settings; Workspace Owners and Admins set the workspace default and can set it for members in bulk.
Who can use this: Every member can change their own visibility; Workspace Owners and Admins can change the default and other members' settings. Basic plan and above, or any plan during the free trial. Works the same for Slack and Microsoft Teams workspaces.
For an overview of the whole feature, read the Celebrations Guide.
The three visibility options
Celebrate Publicly (Recommended): Matter posts a public message in the Matter-connected channel, with any coin rewards.
Celebrate Privately: Matter sends a private direct message, with any coin rewards.
Do Not Celebrate: no message is sent, publicly or privately, and no coin rewards are given.
For members: choose how you are celebrated
Open the web app.
Go to Account Settings, then the Celebrations section.
Choose an option for your birthday and for your work anniversary.
Click Save.
For admins: set the workspace default
Open the web app.
Go to Settings, then Celebrations, then Birthdays or Work Anniversaries.
Scroll to the Default Visibility section and choose Celebrate Publicly (Recommended), Celebrate Privately, or Do Not Celebrate.
Click Save.
For admins: set visibility for many members at once
Open the web app.
Go to Settings, then the Celebrations section, and download the Excel template.
In column I (work anniversary) and column J (birthday), choose public, private, or disabled for each member.
Save the file and upload it in the Celebrations settings.
Click Save.
More on the template: Uploading celebration dates via Excel template.