Yes. The mother of Thomas Mann, Júlia da Silva Bruhns (1851 to 1923), was born in Brazil, on the southern coast of Rio de Janeiro state. The sources cite Paraty as the city of her birth and childhood, and one of them places her mother's family in Angra dos Reis, a neighboring city. Thomas Mann himself was born in Lübeck, in Germany, and never visited Brazil.
Júlia's father, Johann Ludwig Hermann Bruhns, was a German from Lübeck who had sugarcane plantations; her mother, Maria Luísa da Silva, was a Brazilian of Portuguese ancestry, and the English-language Wikipedia also speaks of Indigenous ancestry. The mother died when Júlia was a child, and the father took the children to Lübeck. The girl's age at the move varies between six and eight, depending on the source. In Lübeck she married, at the age of seventeen, the merchant Thomas Johann Heinrich Mann and had five children, among them the writers Heinrich and Thomas. She died on March 11, 1923, near Munich.
What she represents in the work is a biographical thread, more than a declared theme. After winning the Nobel, Mann told a journalist that his mother was Brazilian and that he had inherited his artistic talent from her. In the novella Tonio Kröger, the protagonist is the son of a merchant from northern Germany and of a "Southern" mother, of artistic gifts, named Consuelo, and the Wikipedia article on Júlia da Silva Bruhns points to her as the inspiration. Mann wrote about his mother and Brazil in the text "The Image of the Mother" (1930). Júlia's own memoirs, Aus Dodos Kindheit, published in 1958, idealize her childhood in Paraty.
There are details that the sources describe in different ways: the exact city (Paraty or Angra dos Reis), the age at the journey, and the ancestry of Júlia's mother (Portuguese, or Portuguese and Indigenous). What does not change is that Thomas Mann was the son of a Brazilian woman.