The law on structuring (https://www.law.cornell.edu/uscode/text/31/5324 https://www.law.cornell.edu/uscode/text/31/5324) is about evading the $10,000 reporting

The law on structuring (https://www.law.cornell.edu/uscode/text/31/5324 https://www.law.cornell.edu/uscode/text/31/5324) is about evading the $10,000 reporting threshold for financial institutions taking cash deposits or businesses taking cash payments for goods/services. If they are perpetuating some kind of fraud on Venmo making multiple accounts to do so in violation of the ToS is maybe wire fraud (so is just about everything) but by itself is probably not illegal.