I'm a 30+-year-old engineer. I have been living in the US for 2 years and just got a green card (my employer is really nice).
I'm thinking of doing a PhD (a lifelong checkbox) and I started to apply everywhere, including in Europe. Ideally I would like to do my PhD there, keep the green card and work in the US after, but I wonder if anyone successfully did it?
I initially thought of coming back a week every year but I have read that this doesn't guarantee anything, and I have to prove that the returns were temporary and you still have ties with the US. Is a PhD temporary since it is "fixed" in length?