Keynote doesn't fill the entire external display
Keynote version 12.0 (7033.0.134) running on 14" MacBook Pro (2021) with MacOS Monterey 12.2.1 never fills the maximum extent of external displays when presenting via HDMI.
There is always a black band around the edges.
Changing the slide size in Keynote has no effect.
Exporting to PDF or Powerpoint solves the problem, but eliminates the Keynote animations and transitions.
MacBook Pro (2021)