The Soviet Union had the means, motive, and opportunity to debunk a hoax in real time and chose not to—because it wasn’t a hoax.
Modern Russian and Chinese lunar missions have independently confirmed physical evidence of the Apollo sites.
Chinese lunar probes (Chang’e series) have photographed Apollo landing sites from orbit (e.g., Chang’e-2 in 2010, Chang’e-5 T1 in 2014), showing tracks, landers, and footprints exactly where NASA said they would be.
So there's that.