This is a bad take. Foreigners are usually better off than locals when it comes to these government policies. Arresting one of your own citizens is routine, but arresting an American is a diplomatic problem. The worst that happens is deportation, but he'd probably just get fined or something. And even though that sucks ass it's better odds than most people.
It's not about the locals being nice or even liking you, it's about them hating the trouble it would cause if something bad happened. Even if the government in the US is faggy about the coof, countries don't like diplomatic problems and there are people in America who would make a stink over a Euro country lording it over an American for any reason.
Agreed overall but also disagreed on this point: if there's anything we've learned it's that the normal rules don't apply to Covid fixation by governments and they will do whatever to whoever they so choose so long as they can cloak it "pandemic/public health". All they need to do is ban international (or local) travel and immediately Null is in very serious trouble, or they'll introduce a sudden and drastic fine which would gut expats, foreigners and locals alike. Unpaid fine can lead to trouble with the law, as can not adhering to protracted isolation due to lockdowns.
- America let Americans rot in Chinese gulags and cells for no good reason. They would certainly let Null or some other not-famous not-wealthy American rot, too, for Covid's sake or unpaid fines due to Covid.
- Also you're right that Null could in the worst case scenario maybe get help from sympathetic organizations, but 1) He runs Kiwi Farms and 2) He doesn't want to be made a spectacle of, which is exactly what such a pro-bono organization would want; they'd want to be able to have interviews and pictures posted for publicity
EDIT: and 3) Those organizations can't do anything aside from offer financial help or more likely legal aid, since if a government is dead set on keeping you somewhere you'd have to rely on your own government to make the effort, not just some organization from your homeland, and I doubt any administration--let alone this one--would bother.
TL;DR You're mostly right but wrong about the diplomatic issues, at least by my estimation. It really isn't a matter of locals' opinions but the average American abroad isn't a diplomat and doesn't have the protections of one, even if only because governments don't want to deal with the headache, because there wouldn't be a headache or fuss kicked up by America, particularly with regards to Covid mandates and doubly in the case of someone who doesn't want to become a publicized martyr/victim of Covid mandates.
I could be wrong but having a pessimistic view of the situation, especially in light of how pessimism has proven realistic over the last year sadly, can protect oneself from disappointment and greater trouble otherwise. Everyone, not just Null, should leave any country/state that is starting to hyperventilate over Covid again because we know what's coming.