Hi @Yamen_Zakhour,
Please go to Notes Doctype and Making a Note public will allow you to share it across Users in your ERPNext account. Once you enable making a Note Public, there will be another checkbox, saying 'Notify users with a popup when they log in. You can also select if you wish to give some specific users, the right to read, write or share your note.
Notification for Announcements:
More Information for check it, please.
https://docs.erpnext.com/docs/v13/user/manual/en/using-erpnext/notes
Thank You!