Other question: why don’t they just forge currency? Surely with nation states resources you can create fake currency that easily fools most inspections? Is it that hard to launder cash? Or is the a red line and they are afraid of political measures?

There’s Superdollars but it doesn’t seem to be a really widespread problem so far, right?

Serial numbers of all old dollar bills are recorded when those bills are destroyed and replaced with newly printed bills AND when bills are deposited to banks. Even if fake bill is perfectly made, it will still be detected with this method. Fake and duplicate serial numbers will be detected when compared against official ones.

Forging doesn't scale. No one wants counterfeit for anything close to $1 per dollar. You have to pass off bad bills one at a time.

10 million dollars in $100 bills weighs 100 kg. Distributing and fencing that much counterfeit is probably hard.

They probably do: https://en.wikipedia.org/wiki/Superdollar

There are tons of youtube videos about this. much harder than it sounds to forge at scale. The feds are very good at coming down on forgery. Also, it would provoke strong action by the US, whereas stealing crypto apparently does not.