I have simply not experienced 1) here in denmark. I don't know what to say, I live in a city that's not copenhagen, but if it exists it seems to me it must be rare.

as for 2, yes young people sometimes speak to each other in a mix of english and danish. It's using danish grammar, and critically, not english. You couldn't follow at all if you only spoke english (and with significant difficulty if you only spoke danish for that matter). I consider this similar to the process that creates slang

the other part of 2 regarding people that don't rush to learn the local language. Yes I know people who do this. After living here long enough, especially if they plan to stay, they tend to change their tune. I think there is a lot of motivated reasoning on this topic in particular, including stuff I have said to people myself in the past that friends like to remind me of - Whne I first came here I literally used to talk about how its so hard to practise language because locals won't help while being surrounded by locals who are happy to help. I won't speculate as to why people change after staying somewhere long, its just a tendency I have seen.

regarding 3, it is seemingly often associated with the far right yes, especially when bound with nationalism and themes of invasion/protection, but not unique to those contexts. I have experienced this in leftist political spaces personally, up to the point of votes being held and passing, restricting language in spoken meetings to danish only, explicitly for the comfort of those attending. And of course, I have also experienced this in entirely unpolitical spaces like hobby clubs, discussions at parties, and at work.