Cuba is under embargo. They’re not able to just welcome and take tons of random people who want to live there so I really, really would not count on that happening. They’re a country that has been struggling in the face of US imperialism and embargo for half a century, they’ve recently had wide-spread power outages again, moving there will not help their situation.

China on the other hand is not in the same boat. Learning Chinese is indeed a bare minimum I’d think. As to citizenship, it’s near impossible to get for the average person. The best you can realistically hope for is permanent residency status which gives you most of the rights of a citizen without any political rights and certain others. You can get that after living there for a certain amount of time and applying for it or by marrying a national.

Of the two China is the more realistic plan but understand that China has tons and tons of engineering graduates, it’s a very popular discipline so competition will be very steep and getting a job there on that basis could be tough. I’d recommend having some other angle, a very specialized discipline, perhaps something the west is slightly ahead of China on or something that’s just come into vogue and will have increasing demand but hasn’t hit it quite yet.

And as others mentioned your pay will be much lower than in the US (lower cost of living makes up for it), if you have student loans you need to consider you may never be able to pay them off even with decades of work in China, though as others mentioned if you can move to China, get permanent residence status, renounce your US citizenship and/or simply never return to the US it may not matter if you never pay them off but realize if something goes wrong, if your plans don’t work out and you end up back in the US things could be very rough for you if you have loans you haven’t paid anything into and they go after you.