Earlier quoted context omitted.
Interesting fact. I thought that having an ID card is pretty much mandatory in whole EU. In Slovakia you get one at age of 15 (I think) and it has biometric data - picture and fingerprints. You are not required by law to carry it with you, but it can cause delays if need to be verified by police or other authority. It’s also used to login into e-gov services with a card reader and your pin - but it’s quite limited at…
In the Nordic countries, ID isn't mandatory, and apart from a few border crossings between Denmark and Sweden, there are no border controls either. Apart from the aforementioned border controls, citizens of other Nordic countries aren't required to carry a passport or a national ID card, but should carry some kind of identification on them. In practice, that means you just carry your regular driver's license in your…
Now, there aren't any checks except for the border into Sweden from Denmark, but if there is a check you are not allowed to travel using an ID or driver's license. Driver's licences, ID cards issued by banks or tax offices are not valid for travel within schengen even though you are generally able to move between the countries anyway.
The misconception you present is the reason Swedes with driver's licences and normal ID cards got stranded in Denmark.