Their films “Musk” and “Union Town,” respectively, premiere first at the Venice Film Festival. The TIFF documentary program explores a melange of subjects, from political activists and athletes to cowgirls and winemakers, and even alt-country musicians. “That is the challenge of today’s marketplace, for sure,” TIFF documentary programmer Thom Powers told IndieWire via Zoom. Coming in with a distributor is high-profile filmmaker Gibney’s “Musk” (Bleecker Street, HBO), which is “notable for its scope,” said Powers. The TIFF Documentary lineup will open with Rebeca Huntt’s “Rapinoe,” a profile of soccer star Megan Rapinoe, who led the U.S. women’s soccer team to two World Cup championships and an Olympic championship.