There are considerable Christian and Classical influences in the written sources on Norse Mythology; this is well represented in the academic literature. Themes in Indo-European mythology are also reflected in Norse mythology; particularly the snake or dragon slaying by a thundergod and creation from the destruction of a primordial being; this is discussed by M.L West in his seminal work Indo-European Poetry and Myth. There is also cultural overlap from Celtic mythology particularly in the mythos of Odin and the cultural importance of völvas, M.J. Enright: Lady with the Mead Cup remains the classic work on this topic.
But the deities in "Norse Mythology" being a mish mash of Germanic myths is an exceedingly difficult construct to prove, given the lack of written sources. For example, the Vanir as a distinct grouping of gods/esses, Freya, Loki, Ullr, Bor, Vili, Ve, Heimdallr, Iðunn and the host of minor players in Norse mythology are not mentioned outside of Scandinavian sources. Conversely, there are many gods/esses mentioned in other Germanic sources that are not reflected in the Norse sources.
Odin is connected to the creation of midgard by the destruction of Ymir; according to the Vǫluspá stars, sun and moon already existed but did not know their place. Audhumbla is a quandary in Norse mythology and no connection with Odin can be construed from the existing literature. Frigg being connected to this intial act of creation is your assumption, it is not attested in the sources. Frigg is not Odin's only consort; in Gylfaginning Odin is connected Jörð (Old Norse for earth), with whom he is said to have fathered Thor; Jörð is also called Odin's bride,” in skaldic poetry. Victor Rydberg considered Frigg and Jörð to be one in the same though his work is a little outdated now.
The Norse creation myth does not preclude Frigg being connected to the earth as she is said to be the daughter of the personified earth through birth (Fjörgynn) and her mythos includes that of having enough sway to extract promises from all living things. I don't think anyone is saying that in Norse mythology she is seen as having had a hand in creating Midgard but rather she is connected to the earth through parentage and mythos.
Her association with earth is not ambiguous in Lokasenna she is the daughter of earth. The hypothesis that Frigg and Freya may have been a single goddess is difficult given the paucity of sources. There is an informative video on that subject here:
Provide a refernce from Norse mythology that presents Frigg as a sky goddess or Odin as a sky god for that matter. Odin has many bynames I can't think of one that refers to him as a sky god, in fact one of his kennings is Gracious Lord of Earth. Based on etymological evidence Old Norse Tyr, Old English Tiw are the most likely candidates for sky gods: Tyr evolved from *Dyeus
"Both the name
*Dyeus and the basic Proto-Indo-European word for “god,”
*deiwós, are variations of the root
*dyeu-, “the daytime sky.”[11]
*Dyeus was the quintessential “Sky Father” and likely one of the chief deities of the Proto-Indo-European pantheon. After all, his name was effectively identical with the word for godhood itself. Other gods derived from him include the Greek Zeus and the Roman Jupiter (from
*Dyeus Phater, “Sky Father”).[12] Fascinatingly, the modern English words “day” and “deity” both come from this same root"
Tyr - Norse Mythology for Smart People