This is absolutely nothing to be afraid of, or even give attention, any country can ban anything related to crypto they want, or even crypto in its entire self, but the issue have always been in its implementation.
For example, Nigerian government banned crypto entirely in the whole of the country, but it's citizens still go about crypto like there was or is no ban at all, I believe this will be the same story in Denmark, how are they going to effect this ban? To make sure that citizens don't continue using self custody wallets even after this ban? There is no way to implement such a rule, even if they restrict citizens' access to the domains of those wallets, citizens can always use VPN to bypass such restrictions.
When something is illegal engaging in such activity becomes a criminal offense. Which means one can go to jail for using non-custodian wallets. This is a big problem for people who cherish privacy. So there are many things to be scared of. In my country, the police can search your phone at will, and if they see a decentralized wallet you are a suspect that will be exploited or sent to jail. It is far better not to have this rule in place because trying to invade these bans can be risky. And such laws can hinder crypto adoption because many people wouldn't want to take such a risk.
Well, after reading the update, I am happy that the ban on self - custody wallet rumors turned out to be just an actual rumor, which was all false, but then, as much as what you said did make a lot of sense to me, I still will like to let you know that as much as a government of a country has power over the citizens that they rule over, they aren't at liberty to just do any thing, ban or allow anything they please.
When a government declares a ban on something which everyone knows that them banning that thing was simply for their selfish interest, and not really because that thing is bad, if almost all the citizens of that country ignore that ban and continue to make of use of the thing, trust me, the government will have no choice but to retrace their steps, because it is never possible for a government to send more than half of her citizens to jail, no where has that ever been done before.