Denmark controls the waters of the seaway to Sct. Petersburg and Kaliningrad that are some of the strategically most important ports of Russia.
Blocking of traffic to these would be a severe escalation.
Regularly Russian subs pass through Danish waters - controlled and allowed.
As severe as... say starting the largest war in Europe since WW2 right at our doorstep? Or as damaging our critical infrastructure? Or manipulating our democratic processes?
It's time the West pulls its head out of its ass. We're already at war, whether we want it or not.
I've always wondered how subs handle tidal flows there, and how challenging the tidal flows are.