Grades in Brightspace are not official final grades. Only grades registered in uSis are recognized as official final grades.
Some faculties do not allow final grades to be announced via Brightspace. Please check with your LMS coordinator.
You can export grades from the Gradebook and import them into uSis. This does require modifications to the document. See the articles on Grades for instructions.
It is not permissible to post grades on Brightspace in any way other than through the Gradebook. This is because the combination of student number and grade is considered private. According to the GDRP, such personal data may not be posted without first obtaining permission to do so from everyone on the list.