Hmm. It seems that "America First" just so happens to coincide with a lot of "Denmark first" or "UK first" or "Germany first".

Sure. We're allies for a reason. Our interests coincide a lot. If they always coincided, there wouldn't be any meaning behind a slogan like "America First." Where foreign policy gets relevant is where they don't entirely align.

Like, say, if we want to insist that Denmark should sell us Greenland, and Denmark might decide that's not in their interests. Or if there's an internal dispute between Denmark and Greenland about various matters (like mining rare earth minerals), and what might be in the U.S.' security interest (Greenland mining lots of rare earth minerals) might not be in what they think is their own best interest (preserving the environment).

If you advocate that a nation's foreign policy approach should be somehow more directed to prioritizing that nation's interests rather than those of allies (like "America First"), then it's kind of hard to insist that they shouldn't do the same.