There have been mumblings about mineral wealth, and about strategic bases. None of them really make a lick of sense.
It does not look as if it's serious. But this is a deeply unserious administration, so it's hard to guess.
Possibly to deter Greenland from becoming independent, wt least without guarantees it will stay in NATO and economically within the western sphere.
If they want mineral rights those will be arranged easily with basic diplomacy and investment. They had 17 military bases there during the Cold War and that contract stands. Greenland is under NATO article 5 protection. There is no rational net-positive reason for this no matter what dimension you look in