So this indicates a number less than 20,000 or am I reading it wrong, apologies
I don't think you can determine exactly the figure from a chart like this, it just really shows a trend across the months spanning the virus. I assume the number of published coronavirus deaths is accurately represented by the red area, but what is in question is what makes up the other excess deaths, shown in blue. They could all be coronavirus related, or all totally unrelated but due to some other undefined (to us) causes, or most likely somewhere in between.
The 5 year average line is exactly that, an average, so is subject to outlying data as is every other average.
Don't forget that the X axis is time in months, and the Y axis is numbers, so the 20000+ figure only represents the worst case between the average line and all recorded deaths.
What will be interesting is to see where we are in relation to the average at the end of the pandemic, This will give us a better idea how many people really died of the virus, but obviously it will be an idea only, due to being compared with an average death rate.