ID cards are also a thing, and in principle every grownup should always be carrying ID although its not like everybody really does when walking around the park etc.
There are paper and in-person alternatives to the online services, but the ease and prevalence of the online services makes those actually relatively efficient. The times I've had to do something in person has all been slick.
I think underneath the key concept is that everyone has a unique ID number and means to prove it's them. 99% of the time that ends up being Mobile BankID.