What happens to people who have Skanetrafiken tickets for taking that train to get from Malmo/Sweden up to Helsingor via Copenhagen? Do they have an add-on option for seat numbers, or were they among those passengers who had frustrated the conductor?

It seems like Denmark wanted to avoid having Swedes coming to the airport to hang out inside the airport as part of receiving or sending off flight passengers, and this may be a reason for the approach for train passengers disembarking at the airport instead of for passengers staying on the train and going elsewhere within Denmark. In other words, the measure may have been part of trying to preferably limit airport visitors to just airline ticketed passengers as much as possible.

It’s the EU Digital COVID Certificate all over the place. If I could find a quick and inexpensive way to go to Norway or Finland, I would!

The "EU Digital COVID Certificate" is due to officially launch on 1 July.
https://www.healthcareitnews.com/new...d-17-countries

Denmark to ease travel restrictions: What changes in Denmark this Saturday?
https://www.thelocal.dk/20210621/den...this-saturday/

What tourists need to know about Denmark’s coronapas system
https://www.thelocal.dk/20210624/wha...st-in-denmark/

Sweden: How the Covid Certificate works
https://www.krisinformation.se/en/ha...id-certificate

Norway is connecting to the EU Digital COVID certificate (EUDCC) gateway
https://www.regjeringen.no/en/aktuel...way/id2863309/

Finland Ready to Issue EU Digital COVID-19 Passport
https://www.schengenvisainfo.com/new...d-19-passport/

Did they only check those going to the airport and not those connecting to Metroen?

Finland lets you enter if you are fully vaccinated and arrive from an EU/Schengen country, but the website Raja.fi doesn't say how you should prove that you are fully vaccinated.

Norway’s implementation of the Covid pass is to be applicable to vaccinated US CDC card holders with the Norwegian equivalent of a social security number or other tax/coordination number applicable to those residing in Norway.

Some of both:

There is this still up:

https://www.cph.dk/en/practical/resa...h-från-sverige

But there is the outside waiting area by the T3 taxi stand position.

No. I bought a ticket to Småland on the Skånetrafiken app, and then discovered the note on the platform display about mandatory seat reservations. I asked both the DB guys standing by the machines and the guard on the train, and they both confirmed that seat reservations could not be made with the app, nor were they required. But when the train reached Alvesta, quite a few people boarded with seat reservations for Kalmar.

Perhaps buying the tickets for the Oresundstag via SJ or some other train ticket agents still comes with a seat reservation. Going back nearly 20 years, these trains have had a bunch of seats that had signs above them saying “can be reserved” — even on trains when most or all ticketed passengers on board happened to have no seat reservations. I’ve been displaced a few times and then some because of those “can be reserved” seats having been reserved at time of ticketing (if not later) and my assumption that they would go unreserved as had been most commonly the case for me.

This exists across Europe and it essentially means that the seat hasn't been sold at the time when the information system in the train was updated, but it remains on sale, thus someone can still book that seat. How likely it is to happen then depends on how many people book seat reservations on that particular route - and obviously on regional trains in Skåne and Copenhagen area it's not too common. Unless I'm doing some long distance like Copenhagen to Gothenburg, I wouldn't bother booking a seat.

The (superconfusing) Danish website now lists some countries as green, but there is absolutely no mention of what applies to green countries. Does that mean that normal entry rules apply? In other words, if I live in a green country and I arrive from another green country, can I enter without tests, certificates, quarantine, etc.?

I haven’t read up on the colors, but did receive an email about this:

“OBS (26.06.2021 16:38)
HELE VERDEN: Lørdag den 26. juni igangsættes fase 4 i genåbningen af rejseaktiviteter. Det betyder, at sikkerhedsniveauet sænkes for en række EU- og Schengenlande. Danske turister kan nu tage på ferie i EU og Schengen uden at skulle i isolation, når ferien er slut. Der gælder desuden kun krav om test efter hjemkomst fra gule men ikke grønne lande.”

Udenrigsministeriet, Rejse og ophold, Rejse til udlandet, Rejsevejledninger, USA
https://um.dk/da/rejse-og-ophold/rej...ledninger/usa/

I asked at Hovedbanen’s ticket office, and she has no good answer. One suggestion was to get off once you enter Denmark, but that makes no sense in so many ways.

Has anyone had success entering Denmark on a direct flight from the USA and ONLY the CDC vaccination card and no test? The Danish COVID website seems to suggest that non-EU residents must also have the "vaccine passport" app in addition to their CDC card, I'm currently having trouble figuring out how to do that... or if it's necessary

I have and my wife has. Just the passport and the CDC card. No test and no quarantine. One is US citizen, one is Danish and US Permanent Resident.

No problem for me with CDC card + US passport. Denmark has had its act together on this from the start of opening to vaccinated Americans.

I'll add a third yes (US passport + CDC card only). The other members of my family entered on their Swedish passports and CDC cards with no issues. We still got the tests done just in case of the highly unlikely event of a flight cancellation or diversion to a country where a negative test would've been required.