> I keep seeing this idea that because a company is headquartered in some place, means they don't have to follow the laws of the countries where they operate.

My friend's medium size regional ISP is headquartered in the US and as a hosting company certainly has customers who violate any number of censorship, blasphemy, etc laws in Iran, Russia, Myanmar, Pakistan, Bangladesh, just to name a few.

Signal doesn't "operate" in Sweden any more or any less than any other internet based service which has zero servers, offices, bank accounts or other physical presence in the country.