I don't think technical knowledge really comes into play here, which is exactly why it's causing such anxiety. If you're a U.S. citizen, enough of your identity is available for sale that this could happen to you, and there's nothing you can do about it.

You can't keep your PII safe because government and financial institutions have it, have already lost it repeatedly, and keep exposing it. You can't prevent these types of accounts from being opened because credit blocks and monitoring don't come into play with them. You can't monitor it yourself because the accounts don't show up on credit reports and there's no way for you to find out they exist.

The victim in this case was randomly selected. It could have been any person in the country, because literally every single one of us has had the minimum info needed to create a Cash App (et. al) account leaked at least once. Some people commenting here have probably had accounts opened in their names and never knew about it, only because the police weren't as malicious as the guys handling this case, or didn't feel like bothering to investigate at all.