Government bonds. There were ETFs holding Greek gov bonds for example. Greek cheated to enter the EU (by fudging its numbers, with the help of big accounting firms and banks). And government bonds are known to be risky, seen that throughout times many government have simply grown their public debt and then defaulted.
Fun fact: US public debt grew from $33 trillion (with a 't') to $34 trillion in ... drumroll ... 100 days.
Woot!
P.S: I'm not sure your question is correctly phrased... 3% to 5% of the world's entire GDP is linked to crime. By now it's not even clear if 3% to 5% of all the Bitcoin transactions are linked to crime.
I should've added this comment from the SEC, the entity that just authorized this ETF:
"""
Though we’re merit neutral, I’d note that the underlying assets in the metals ETPs have consumer and industrial uses, while in contrast bitcoin is primarily a speculative, volatile asset that’s also used for illicit activity including ransomware,[4] money laundering,[5] sanction evasion,[6] and terrorist financing.[7]
"""
- https://www.sec.gov/news/statement/gensler-statement-spot-bi...
What other ETF exists for an asset that the SEC closes its statements about like this?
https://www.justetf.com/en/etf-profile.html?isin=IE00B4X9L53...
"""
Though we’re merit neutral, I’d note that the underlying assets in the metals ETPs have consumer and industrial uses, while in contrast bitcoin is primarily a speculative, volatile asset that’s also used for illicit activity including ransomware,[4] money laundering,[5] sanction evasion,[6] and terrorist financing.[7]
"""
- https://www.sec.gov/news/statement/gensler-statement-spot-bi...
What other ETF exists for an asset that the SEC closes its statements about like this?