Two things.
First, I'm not 100% clear on what "just how much" even means...what precisely does adding the word "just" to "how much" mean?
Second, is the bold usage of "just how much" in combination with "overstate" OK?
https://join.substack.com/p/what-does-canada-do
Regarding Iraq, the illegal invasion—which was an act of unprovoked aggression—unleashed sectarian tensions, produced ISIS, and led to all sorts of hideous and horrifying bloodshed. The entire region was doused in blood and destabilized—it’s very difficult to overstate just how much damage the aggression has done and continues to do.