Reason and duration irrelevant. A sign could be that all flights are cancelled, diverted, and delayed across the country, but likely there will be an announcement due to weather/ war/ instability/ etc. Only countries with two or more international airports count, otherwise this would be trivial.
Resolves YES if every one of an EU country's international airports are shut down at the same time, beyond regular hours. Nightly closures don't count. Smaller private and business airports don't count.
Resolves NO otherwise after close.
Dependent states like Greenland, etc. don't count for this; must be a sovereign nation (such as Greenland's parent state: Denmark).
Iceland has more than two international airports. 1) KEF, obviously 2) AEY has regularly schedules international passenger flights to the UK, Switzerland and the Netherlands 3) RKV has scheduled flights to Denmark/Greenland.
But Iceland isn’t in the EU and that’s why it doesn’t qualify for this question.