I don't have a canned script for the Drive overallocation error/warning.
If the error/warning is posted to the logfile, then you might try sending Pushover notifications via the 'Status alerts' action set (see screenshot).
Be warned that I don't see a way to filter for specific errors or warnings, so there might be situations where the notifications become excessive. For example,
Blue Iris can generate 100's of 'Signal: Failed to connect' warnings if a camera or your network has a issue,
View attachment 203110
I'll add this idea to my future projects to consider list. I'm imagining periodically scanning the Blue Iris logfile's most recent error/warning lines for user-specified entries.
It would be helpful if you could post a screenshot of the line(s) from the logfile (*.txt) containing this error/warning.