Running Win Server 2019, we had to 1st create/schedule the local backup job in QB.  Then to Windows TASK SCHEDULER to modify them.  Click on the TASK SCHEDULER LIBRARY, then see all the tasks in the middle pane.  Find your QB backup task and then right click to PROPERTIES.  Modify:

1.  Bottom left: check the box that enables RUN WITH HIGHEST PRIVILEGES

2.  Bottom middle: select the Windows version you are running (I selected Windows Server 2019)
3.  Click OK

Right hand pane of the TASK SCHEDULER: you can click the RUN button if you want to test your new task...
Note: do not modify your tasks inside of QB; use the task scheduler to modify them.