Manichaean Letter Sadhe

It is a letter in the Manichaean alphabet, used within words.

Manichaeism, the religion associated with Mani, began in Babylonia in the third century CE. The Manichaean script developed from related Syriac Estrangela (an early Syriac writing style) and Palmyrene Aramaic traditions; it was an adaptation, not a script with a securely attributed single inventor.

It served to write Middle Persian, Parthian, Sogdian, Bactrian, and Old Uyghur. Religious books carried Manichaean teaching, while Central Asian manuscripts also used it for books, hymns, and translations. Related Aramaic bowl writing is dated no later than the beginning of the seventh century, but those bowls are not securely identified as Manichaean; later Central Asian manuscripts clearly are.

Why does 𐫝 change beside other letters?

Its right-to-left shaping controls the connected form.

Manichaean is written right to left and uses contextual joining: letter shapes connect according to their neighbors. Sadhe is a right-joining letter, so it can connect with the letter on its right. The pair with Manichaean letter yodh (𐫏) and the pair with letter nun (𐫗) each have an obligatory ligature, a required combined written form.

Without a font and text engine that support Manichaean shaping, a connection may fail to appear or the character may be missing. That is a rendering limitation, not a new meaning.