My understanding is it’s the earliest known alphabet but not the ancestor to all alphabetic languages as there are Asian and other alphabetic languages that are not derived from western or Arabic alphabets. Specifically Greek and Latin alphabets and their descendants are based on it. Specifically Japanese Hiragana and Katakana are syllabic alphabets derived from kanji (and Chinese pictograms) as a simplification of the pictographic language and not derived from proto sinaitic. Others are possibly linked, like Thai, Khmer, etc through an Aramaic -> Brami-> Pallava->Khmer linkage but the Brami link is not fully established to be true.
No: most scholars believe alphabets were only invented once, much like the wheel. All Western alphabets are direct descendants, and the non-Western alphabets were directly inspired by it. [1]
Phonetic alphabets were introduced to most of Asia by various Brahmic scripts; the most widely-used (albeit briefly-used) one being the Mongolian Phags-pa script [2], derived from Tibetan, derived from various Brahmic scripts, derived from Aramaic, derived from Phoenician, derived from — sure enough — proto-Sinaitic. Thai and Khmer are derived from Pallava [3], which is derived from Tamil-Brahmi, derived from other Brahmic scripts, again derived from Aramaic and thus eventually from proto-Sinaitic; etc etc.
1: https://en.wikipedia.org/wiki/History_of_the_alphabet
The wheel was independently invented in the Americas, it just seems to have been used exclusively for toys:
https://en.wikipedia.org/wiki/Wheel#/media/File:Remojadas_Wh...
Syllabaries are not alphabets.