It's been circulated before. It's one of these forecasts that uses certain parameters to model possible future scenarios. These are weighted in certain ways. Since war and civil unrest leads to refugees, in a generalised global model accepting large numbers of immigrants is modelled as spill-over of war and civil disorder, and massively pulls down the projected HDI. It means if you are an immigration country, you get a long-term forecast from these people indicating you will sink like a stone in HDI. It's a reasonable assumption when modelling parts of the world where spill-over effects of neighbouring countries imploding leads to massive waves of refugees, which masses up the neighbourhood. Sweden is an international outlier in that respect, since it's not taking refugees and immigrants because Norway or Finland has blown a gasket and are collapsing.
Given the length of the projections, if this model had been used on say the 19th c. US, it would today by logic default be a third-world hell-hole. There's a good many similar studies from various parts of Europe clearly indicating how for all the frictional problems immigration can cause, it leads not net gains for the nation accepting it. Sweden has spent the last 20 years growing its economy faster than then rest of the EU and even the US. Each new million citizens mark has been passed at a faster rate than ever in Swedish history. It's projected to get a coming old-age dependency rate well ahead of the rest of an otherwise quickly greying Europe. That's one of these question one can pose to the selection criteria: immigration is super-bad, apparently, but ending up with a sliver of a population not decrepit from age, tasked with supporting a huge lump of steadily deteriorating old people is apparently no problem at all, m'kay?
This study is being trotted around the internet becuase the model settled on by a quirk of selected criteria and their weighting threw up a result supposed to be very unflattering for Sweden. It means Sweden is an immigration country these days. We knew that. Everyone who wants to close the national borders hates it of course.