atAll: Is it @ everyone?
Textarea: The mobile phone number configured in DingTalk, used to @ mention the corresponding person. Separate multiple values with commas or line breaks, supports environment variables.

With Notify everyone ticked the mobile numbers are no longer added to the message — everyone is notified anyway.
Only members of the group can be mentioned; DingTalk masks the number of anyone who is not.
DingTalk does not highlight a mention in a Markdown or ActionCard message, and it is not tappable on the mobile client — the notification itself is still delivered. This is DingTalk's own behaviour.