Reddit reviews Mozart: A Life

Motzart became Mason in 1784, he passed in 1791. He joined lodge lodge Zur Wohltätigkeit, which is roughly Beneficence. In 1785 he composed a Masonic funeral March (Maurerische Trauermusik), catalogued as K.477 (alternatively as K. 479a), and wrote and performed several other Masonic pieces.

According to Maynard Solomon, Masonry remained an important aspect of Motzar'ts life.

Despite being wikipedia, this summary is actually decent
https://en.wikipedia.org/wiki/Mozart_and_Freemasonry

EDIT: Motzart's lodge(s) seemed to align with the humanism and rationalism of the Strict Observance (I don't know if it was actually in allegiance to von Hund's body), unlike the other big Masonic bloc in Germany during this period, the Gold- und Rosenkreutz, who were of a more occult and alchemical mind.