How it would have fared an alternate Kalmar Union between Norway, Denmark and a Kingdom of Germany non linked to HRE, formed as opposition to an expanding Sweden which would dominate most of the Baltic (Finland, Baltic states, Prussia, Further Pomerania...)?
First, its honestly impossible to have a Germany not linked to the HRE unless the Empire itself were abolished, or dissolved as a result of a successful war, and this is unlikely given the fact that the Imperial Knights would not likely submit to a Danish-dominated Kalmar Union. And if the Hapsburgs are the emperors, then its even more impossible.
Only plausible way for such to happen is if Denmark-Norway allied with France, but France was OTL allied with Sweden. so circumstances would have to be such that France sees more value in a Danish alliance than a Swedish one.
Then there's Poland-Lithuania. While they might lose the Baltic littoral and Prussia, they would be motivated to regain those territories, and if the Hapsburgs should be displaced as emperors, they could find a new home in the Commonwealth. The Austrians would want to regain their hausmachts (house territories) back and Poland wouid want the Baltic Coast back in their hands. They could even ally with Muscovy-Russia for the purpose.
Let's also not forget the future Dutch or England. The English would see the domination of the North Sea and English Channel as a threat to their security, prompting them to bury the hatchet with France and even begin supporting Dutch rebellions which could break out sooner than OTL. I would suspect that when Protestantism becomes widespread, there would be an alignment of sorts happening and the earlier outbreak of the 30 Years War