An Azure relational database service.
I am assumming you are talking about automated backups. I am afraid you cannot monitor automated backups using PowerShell.
However, you can use Extended Events for that purpose.
CREATE EVENT SESSION [Simple backup trace] ON SERVER
ADD EVENT sqlserver.backup_restore_progress_trace(
WHERE operation_type = 0
AND trace_message LIKE '%100 percent%')
ADD TARGET package0.ring_buffer
WITH(STARTUP_STATE=ON)
GO
ALTER EVENT SESSION [Simple backup trace] ON SERVER
STATE = start;