Still a U.S. citizen. That's something you...probably don't want to give up. Because while it's a pain at times, there are international benefits to it (and once you give that up, you're probably never getting it back, which means even visiting the US becomes a pain). Although there's no escaping paying federal taxes. Residency/tax residency is going to depend a great deal on what country you go to.

Argentina is kind of a mess at the moment, so I'm not a tax resident. I'm currently looking to move to Spain or Malta on a digital nomad visa and both of those are different. In Malta, I'm not a tax resident on that visa, but if I want to stay long term (I can stay for up to 3 years on that visa) I'd need to transition to a different visa. With Spain, I would be a tax resident on a digital nomad visa and would have to pay Spanish tax (although they have an agreement with the U.S., so I can take that out of what I'd pay to the fed)....the Spain visa can also lead to permanent residency.

Basically...there's lots of options out there. If you can work remotely (which I've been doing for 15+ years now), it makes it pretty easy to move to another country. If you're curious about doing it yourself I've written other material about the topic which you might find helpful.