The United States is one of only two countries (with Eritrea) that taxes its citizens on worldwide income regardless of where they live. Move to Portugal, retire in Mexico, settle in Thailand — you still file a US federal return every year. Forever. The only way to escape is to renounce US citizenship (irreversible, has its own tax consequences).
What changes when you move abroad: you may also owe tax to your country of residence, but the US-side obligation continues. Tax treaties prevent double taxation by allowing credits for foreign tax paid. Smart structure can result in net tax LOWER than you'd pay in the US.
What does NOT change: the IRS expects you to file. Missing FBAR or filing requirements has aggressive penalties (up to $10K per violation for non-willful, $100K+ for willful).