There is a difference between "not being able to leave" and "not being able to enter", your examples are of second kind. Currently there are very few places that prevent people from leaving, e.g. North Korea, Turkmenistan, Xinjiang for Uighurs. East Germany and USSR in recent history.
Most countries have laws that strictly limit who can entry. What good is the theoretical freedom to leave, if there is no where to go?
Compare someone from Venezuela and North Korea. Millions of people managed to leave Venezuela and stay alive, unlike millions of people from North Korea who had died from hunger in 90s despite having neighbours ready to take care of them.
But if you think that there is nowhere to go, you need to support seasteading, because if it succeeds there will be many new countries that will be happy to take new citizens.
And as we're seeing on the US southern border right now, the rules are very, very different for people who want to pick and leave, say, Guatemala.