Arabic Letter Ṣād Final Form

No. It is Ṣād in a joining form. Ṣād is a consonant commonly written as ṣ in Latin transliteration. In Arabic it contrasts with Sīn س. Persian loanwords containing Ṣād are generally pronounced with /s/, and some Egyptian and Maghrebi varieties merge its pronunciation with Sīn while keeping the spellings distinct.

Arabic writing developed through earlier Nabataean forms. The earliest dated inscriptions with a full repertoire described by scholars as Arabic appear in the late fifth century CE. Ṣād also has historical correspondences with Phoenician Ṣade and Hebrew Tsade. These connections belong to the history of the base letter ص, not to this pre-shaped character.

How do I type Arabic Ṣād in its final form?

Type ص and let the text shaper choose its form. Arabic letters change shape according to how they join their neighbors. A final form joins on the preceding side but not the following side, so it can appear inside a word before a letter that does not join onward. Fonts may draw the form differently.

ﺺ is a pre-shaped compatibility character retained for older encodings. Under NFKC normalization it becomes ص: the stored joining shape is removed, but the letter identity stays the same.