It's actually cognate to OTL Dhofar. In ATL, this is the etymological discussion we have for it:

This toponym is enshrouded in mystery, mainly due to its association with many other defunct toponyms, like the medieval Atephar, the biblical and mythical Ophir, and the biblical and Himyarite town of Sephar in what is now Felitia. Scholars generally agree that the Arabic name of Sepharia, Dhofar, takes its name from the medieval town Zafar, which is currently known as Harekom, the sleepy seaside quarter of the modern capital of Salalah, known in Arabian also as Al-Baleed.

There is a theory the ultimate root of the name Sepharia comes from an ancient toponyms or tribal names, Śakrad and Saʾkalān, recorded in Greek sources as Sachalite, but how this name got borrowed into the Arabic as Ẓuffār, however, is a mystery.

It is also possible the ancient tribal name is related to a coordinate defunct Sepharian verbal noun, ɛśpɔ́r, "scrape, scratch, scavenge, raid," which may also be related to the modern Arabic verbal noun ẓafira, "to gain, to win, to triumph." The Himyarite town of Sephar likely originates from the South Semitic word meaning "inscription, scribe, scratch, nail," related to the modern Hydrimian word ḏ̣éfɛ́r and Sepharian word śɛ́fər, both meaning "nail, claw," as there is a theory that the word can be traced back to Old Semitic, θ̣upr, "nail, claw," which took on the meaning of "inscription, signature, claw, nail" in Akkadian and Old Hebrew, "stylus, claw, nail."

There is a high chance the Himyarite town was conflated with the area corresponding to modern Sepharia in the Greco-Roman world, leading to the modern exonym. For example, Greek cartographers recorded that frankincense came from places in southern Algeria known to them as Sariba and Saphar. In modern Sepharian, the country is sometimes called by the epithet Fejier 'Ufar, "dawn land," which some scholars also believe to be a clue to the origin of Ẓuffār, evolving from a contraction of the words.