Adding points to line chart to indicate an event in the data set, based off a condition?

Hello,

I have a historical data set plotted on a line chart (2011-2021), with a primary and secondary y-axis. Every x amount of data points (x not fixed), both of the y-values go to zero, indicating a "shut-in" occurring at that specific date.

Every time a shut-in occurs, I want to annotate this on the plot, whether it be through a data label "shut-in", or adding points on the plot (circle/square/diamond..etc. - doesn't matter), with that point being added to the legend to indicate it's representation.

Is there a way of doing this efficiently? I have a very large data set and it would be tedious/ineffective to do this manually.

See attached excel example for reference.
Thanks,

K

The first thing that came to mind is a technique like this (https://peltiertech.com/Excel/Charts/FormatMinMax.html ) where you add another data series with the values for the "shut-in" data only (a bunch of N/A for the other points), then format this new data series as desired. The tutorial appears to have been written for Excel 2003, so some of the commands may be in different places, but the basic idea should work.