Ancient South Arabian script is defined in Wikipedia, as:
[The ancient Yemeni alphabet (Old South Arabian ms3nd; modern Arabic: المُسنَد musnad) branched from the Proto-Sinaitic alphabet in about the 9th century BC. It was used for writing the Old South Arabian languages of the Sabaic, Qatabanic, Hadramautic, Minaic (or Madhabic), Himyaritic, and Ge’ez in Dʿmt. The earliest inscriptions in the alphabet date to the 9th century BC in Akkele Guzay, Eritrea. There are no vowels, instead using the mater lectionis to mark them.
Its mature form was reached around 500 BC, and its use continued until the 6th century AD, including Old North Arabian inscriptions in variants of the alphabet, when it was displaced by the Arabic alphabet.
In Ethiopia and Eritrea it evolved later into the Ge’ez alphabet, which, with added symbols throughout the centuries, has been used to write Amharic, Tigrinya and Tigre, as well as other languages (including various Semitic, Cushitic, and Nilo-Saharan languages)].
The Ancient South Arabian script was very developed and in wide use. So, Why Arabs Did Not Use Arabic Alphabet to Record the Holy Quran? and instead somehow someone developed a new alphabet borrowed from the Nabataean alphabet which was primitive and foreign.
The Arabs of Southern Arabia converted to Islam very easily and peacefully and they were strong sincere supporters of the prophet (pbuh) contrary to the people of Hijaz and the rest of Arabia. But, after the death of the prophet during Rashidun Caliphate and the Umayyad state the Quran was collected and written.
The Umayyad regime was founded by Muawiya ibn Abi Sufyan, long-time governor of Syria, after the end of the First Muslim Civil War in 661 CE/41 AH. Syria remained the Umayyads’ main power base thereafter, and Damascus was their capital.
The Umayyad caliphate was marked both by territorial expansion and by the administrative and cultural problems that such expansion created. Despite some notable exceptions, the Umayyads tended to favor the rights of the old Arab families, and in particular their own, over those of newly converted Muslims (mawali). Therefore, they held to a less universalist conception of Islam than did many of their rivals.
The Umayyads continued the Muslim conquests, incorporating the Caucasus, Transoxiana, Sindh, the Maghreb and the Iberian Peninsula (Al-Andalus) into the Muslim world.
The earlier Turkic settlers in Northern Arabia must have played crucial role during that period that resulted in the demise of ancient South Arabian culture and influencing the creation of new form of religion based on aggressive expansionism and Turkic traditions.
The Arabs wrote before Islam, since the ninth century BC to the seventh century AD, 60 years after Islam. This is their ancient alphabet.
The next image is of ancient Arabic rock scripts in Arabia. This how the Southern Arabs used to write for more than a thousand year, now this people are called “Extinct” Arabs, for no good reason, and they were replaced by the so-called Pure Arabs (or Qahtanites) and Arabized Arabs (or Adnanites). A fictitious grouping and classification during the Umayyad period.
This is a major alphabets tree map showing that modern Arabic is not of Arabic origin.
Should the Holy Quran had been written in original Arabic it would have used the Ancient South Arabian alphabet that existed since 1300 BC until 60 years after Islam and was extinct in 700 AD in Arabia, but it is still developed in Ethiopia and Eritrea now.
The present Arabs, Arabic language, and Islam are NOT the true Arabs, Arabic language, and Islam. That is why they are fighting and terrorizing in many countries. What we have today are Turkic versions of Arabs, Arabic language, and Islam.
This history is exactly what links the rulers of the so-called Arabs in Arabia, particularly Saudi Arabia, Qatar, Bahrain, Jordan, Palestine, and Kuwait, with the Turkmen in Syria, Lebanon, and Iraq together with Turkey in supporting terrorism against the peoples of Syria, Iraq, Lebanon, Libya, and more remarkable against the truly Arab Yemen.