Do migrants do jobs that native-born citizens would not under any circumstances do, or do they do jobs that native-born citizens would not do for the low wages that migrants are willing to accept?

This really depends on the quality of the migrants coming.

The immigration policies of my home country Sweden has been detrimental for the Swedes.

I live in Zürich and there are a lot of foreigners here. Here it’s not so clear cut if it’s for the better or for the worse.

Regarding the taxation argument. That may have been true in the past (it doesn't account that many of these people stay and then will need to supported when they become elderly) but under the "Boris Wave" immigration boom that is no longer the case.

It doesn't address the other problems such as social cohesion.

>Plus they often do jobs that many people wouldn't otherwise

because the wages are low, why are the wages low? because these jobs have access to an unlimited amount of strikebreakers/migrants willing to do them for those low wages, so the wage stays suppressed and low, instead of allowing market mechanics to bring those wages up