Sweden did NOT flatten their curve, it peaked much higher than that of countries which had a lockdown. Their policy was specifically NOT to flatten the curve, but to go for herd immunity.
No, no, Sweden actually tried to flatten the curve until their idea of herd immunity had been achieved: The idea was that the vast majority of people had to get infected, that there was no way around it, so you might as well do nothing to prevent everybody from getting infected, but you should try to flatten the curve, so the hospitals weren't overwhelmed by a sudden number of Covid-19-sick people that they couldn't possible handle all at once. So by flattening the curve, they wouldn't try to prevent people from getting infected. They would merely prevent almost everybody from getting it at the same time.
The exception this 'strategy' was that old people should be protected while the rest of the population got infected and thus achieved a hypothetical level of immunity.
As we have seen, Sweden did manage to flatten the curve a little, but not nearly enough to prevent the hospital system from becoming overwhelmed; cf. long-distance triage and palliative care, i.e. opiates, I assume. And Sweden also succeeded in having so many people infected in the capital that it is not at all unlikely that Stockholm's R
0 will have been lowered considerably at this point due to the subsequent immunity, whether permanent or temporary, but it is really hard to tell if that's the case, and it probably also depends on the respective neighborhoods you live in since poor neighborhoods in Stockholm with many immigrants had an awful lot of cases, whereas affluent neighborhoods didn't, so they also can't have many people with infection-induced immunity.
And many small communities in the rest of the country probably never had the number of cases that they had in Stockholm, so even the level of partial immunity in the country is probably not equally distributed, i.e. high level in Stockholm and other places with a high death toll, lower in areas with a low death toll.