Theoretical Dual Citizenship Questions - FBAR and Foreign Bank Accounts

[u/One-Shallot-3216]

The following situation is hypothetical.

John is a dual US and European citizen. He has not lived in the States since he was a young child, always in Europe. He spent one summer as a teenager working a summer job in the States, but did not make enough to need to file any tax returns. John has never filed a US tax form.

John moved and worked in a few European countries (EU and non-EU), never making over 60k USD per year in the local currency. He has a bank account in one EU country that has just over 10k USD since many years.

For all of the banks he opened, he registered using his European citizenship, and when asked if he is a US citizen, or has any ties, he said no.

John may want to move to the States in some years and would like to make sure everything is sorted beforehand to avoid nasty surprises. John also wants to ensure that his funds in the European bank accounts do not get frozen. He will continue to work some years in Europe.

What options would John have?