The people in Lebanon and Venezuela trust that the US government will continue to exist and that they will either meet with people who want to do business with it, or will meet people who assume they will meet people who will, etc. So they have value.

So if people trust that Bitcoin will continue to exist and they will meet people who want to do business with it etc...

except bitcoin is one of the worst choices for that purpose

even the Iranian Rial is more reliable

can't edit anymore, the point is Iranian Rial is accepted by 90 million people in Iran, all the Iranian businesses and the Iranian government, there are much less bitcoin users, technically there are a lot more accounts, but that doesn't mean real people or real businesses.

Not surprisingly Iran and Russia are teaming up to create a new stablecoin and not adopting BTC, because using BTC right now is literally the best way to get caught (for example infringing sanctions).

The people that can afford to trust and use bitcoins for exchanges are the people who do not have to fear the surveillance of State actors/secret services/national agencies(NSA,FBI,Europol,China's central bank,...)/etc and that would be much better off using another FIAT currency (USD, EUR, etc.)

That's the only thing that gives Bitcoin value. So, in a crisis it can become false for some people, then spread to the people they know, etc.

With dollars, all Americans need them. So do international companies that transact with Americans. If you think the US government will hold, then that belief will be true, it's only a question of the number of steps.

> in a crisis it can become false for some people

it depends on what the crisis is, and whether this same crisis also makes people believe that the US gov't will not hold.