This character is a Other Letter and is mainly used in the Arabic script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written as Arabic letter from right to left. When changing direction it is not mirrored. The word that U+0679 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with one other glyph.
The Wikipedia has the following information about this codepoint:
Ṭe is a letter of the extended Arabic alphabet, derived from T (ت) by replacing the dots with a small t̤o'e (ط; historically four dots in a square pattern, e.g. ٿ). It is not used in the Arabic alphabet itself, but is used to represent an voiceless retroflex plosive [ʈ] in Urdu, Punjabi written in the Shahmukhi script, and Kashmiri as well as Balochi. The small t̤oʾe diacritic is used to indicate a retroflex consonant in Urdu. It is the fifth letter of the Urdu alphabet. Its Abjad value is considered to be 400. In Urdu, this letter may also be called tā-ye-musaqqalā ("heavy te") or tā-ye-hindiyā ("Indian te"). In Devanagari, this consonant is rendered using ‘ट’.