Just yesterday I went to a Forex bank branch (as I thought no other bank dealt with cash in Sweden) in an attempt to exchange a few 500 euro bills for kronas. And I could not, and the clerk said that in Sweden it is not possible to exchange 500 euro bills since 2018, and that the only thing to do is to go to a euro zone country (such as Finland). Is it true that in Sweden there is no way to exchange (or change) a 500 euro bill?
While still legal tender in the Eurozone, since 2019 the 500 euro note is no longer issued by the European Central Bank, so it's getting harder to find merchants that accept them, and it was always inconveniently large from the beginning. Sweden is also, famously, the world's most cash-free society, which doesn't make things any easier.
That said, while neighboring Denmark has officially banned the use of 500 euro notes, as far as I can tell Sweden has not followed suit. So I'd suggest you ask/call around at other money changers and banks, and see if you can find somebody willing to accept it -- Forex is not the only game in town.
As stated, the notes are not very common.
But let me classify that: they're not very common outside of criminal circles. They're mostly now used by criminals for large transactions (drugs, weapons, human trafficking). As a result most banks and almost all other companies reject them out of hand because they don't want to get involved in money laundering schemes. And that's if the employees in question even recognise them as many will never have seen one.
So yes, they are technically still legal tender in some countries but so uncommon that they're effectively useless. And Sweden not being in the Euro zone means they may not even be legal tender there at all, and if banks accept them they'd do it only as a courtesy (and then themselves have trouble getting rid of them).