Are any of the portals discovered by NASA in Earth’s geomagnetic field used or created by extraterrestrials, and if so, in what ways?

As you saw intuitively, these so-called portals are merely fluctuations in the Earth’s magnetic field intensity and are not true portals. It is a kind of catchphrase designed to create interest and pique the imagination, but has no relevance to extraterrestrial needs or actions. They indeed are perturbing the geomagnetic field in various ways. This is, in part, the reason for the fluctuations but it is not something akin to what is in the science fiction screenplay allowing aliens to transport themselves to come and go from other dimensions, locations, or times.