Honestly, I get the impression your objective is to get a foot in the door for a certain idea, so to speak. Concern trolling ("just" preservation of Danish culture, huh?!), constructing a narrative where legitimizing neonazi parties through compromise is without alternative. You are not even addressing the foreign influence with these movements, the threat of social media reality distortion. Although, you tried to preemptively diffuse political association, I don't believe you are arguing in good faith. My answers are meant for everyone else reading, since I think it's wasted on you.
The CDU ran their election campaign on "anti-immigration" and continues to perform this rhetoric. So far the AfD poll numbers have been climbing, so ... your premise is evidently just wrong. This has been debated to death and I think for the general case, political science agrees that people will choose the original, when moderate parties pander to populist ones.
I am not familiar with the Danish situation. It's a very small country, with little land borders. Germany is large, bordering nine countries. It has a very high population density, large global economic influence, and a very unique history in regard to unification as German Reich, industrialization, revolution, fascist and communist dictatorships, war and division, and contemporary reunification. There is a very, very distinct geographical correlation with AfD voters and the former DDR territory.
Most people here are very fine with Germany's lack of nationalism and flag identity. We never really had a unified cultural or religious identity, since what's considered "Germany" has been quite radically changing in the last 300 years. (I think Rammstein's "Deutschland" does quite a good job expressing this feeling: https://www.youtube.com/watch?v=NeQM1c-XCDc)
You are also suspiciously discounting the impact these populist narratives and policies have on the lives of those matching the appearance of the scapegoat targets. Overall the neonazis' demands are not "just" a "sane" immigration policy, but open calls in particular for deportation, even deportation of German citizens. And they are also calling for de facto suppression of women's rights and LGBT lives all together. Oh, and what about the newly found Russia fandom and climate change denial? What's your take here?
Should we give in there as well? And if not, what's the difference?
If you want to win AfD voters, what you fundamentally have to do is present a vision that inspires AfD voters and convinces them to join your side.
Does this mean adopting AfD positions and trying to water them down a bit? Not necessarily, I agree that populist-lite is always going to lose to the original. But it means convincing immigration skeptics, gender traditionalists, perhaps even Russia fans and climate change deniers that they're allowed to be on your side. It's a hard but necessary line to straddle. I struggle with it myself - I spent a while over the weekend trying to find some good flyers to leave on people's Teslas, until I sat down and asked myself why none of the major protest organizers are encouraging this.
And once you start thinking within the realm of strategic moderation, immigration sticks out as an obvious compromise to make. Restricting immigration has few catastrophic downside risks, is easy to roll back if circumstances change (unless you do it in a catastrophic Trumpian way...), and unless your population pyramid is really unhealthy doesn't involve many tradeoffs with other policy areas.