[4][5] In 59 games for the High–A Lansing Lugnuts, Millas hit .255/.372/.359 with 3 home runs, 28 RBI, and 10 stolen bases.

[6] On July 30, 2021, the Athletics traded Millas to the Washington Nationals with Richard Guasch and Seth Shuman for veteran catcher Yan Gomes and utilityman Josh Harrison.

[7] Millas was assigned to the High-A Wilmington Blue Rocks after the trade, where he hit .284 in 27 games.

In 88 total games, he batted a cumulative .225/.340/.350 with 6 home runs, 36 RBI, and 8 stolen bases.

[10] Millas began the 2023 season with Harrisburg before being promoted to Triple–A Rochester Red Wings in late May.