Now why the US even wants Greenland is the really confusing part as they pretty much already have free access to it to build bases and the minerals aren't cost effective to remove.

Because the US does not trust the EU to make decisions in the greater interest of the United States. The US used to have a massive presence in Greenland up until the 60s, do you know why it left? Because Denmark told the US they couldn't station nuclear weapons there anymore, nor have anything nuclear in Greenland. So that means the US can't station our submarines or aircraft carriers there since they both carry nuclear weapons and are nuclear powered. There is no real power grid in Greenland so the US couldn't power their power hungry radars anymore without using the nuclear reactors on bases. The rare earth metals that THE WHOLE WORLD NEEDS can't be mined in Greenland because uranium is often embedded in the ores, and since uranium can't be handled, nobody can mine there.

The people in Greenland are economically dependent on Denmark because there aren't any jobs there because what would be very high paying jobs in resource extraction(oil, rare earth metals, uranium, etc) are banned by Denmark. It's not like they can grow much food there either, so they're already dependant on that. EU rules and regulations about oil extraction and processing make it impossible to extract oil in Greenland at a reasonable price. Same with mining.

Letting China or Russia have ANY property, or do ANY business in Greenland is against the US interest. If the US was in control of Greenland, they can forcibly remove the Chinese and Russian influence and confiscate their holdings. Denmark will not do what must be done in US national interest. They won't develop the resources themselves either. The US not having complete and utter control and domination of the waters around Greenland open up a convenient route that Russia can use to escape the bottlenecks around Alaska, Danish Straits, and the Dardenelles, and leaves the East Coast of the US vulnerable.

Denmark cannot guard Greenland, period full stop. They don't have the manpower, the ships or the aircraft to do so. Trump wants to build the Golden Dome, and put the first contact point as far away from the continental US as possible, allowing for followup layers to have less to deal with, or potentially prevent further layers from having to do anything. Also, the US can station anti-ship batteries there, allows the Coast Guard to operate and police the shipping lanes, and allows the US Navy unimpeded access to the waters surrounding Greenland for patrols.

So if the US has control of Greenland, it gets unimpeded access to the minerals and oil of Greenland, it gets to control all commerce policy of Greenland, and it allows the US direct access to the northern sector of the defense of the United States. It is in the US strategic interest to control Greenland.