If public viewings are held, participants will want to cheer out loud.

If they are held outside with proper distance between spectators they would not be so problematic, but if the organizers can't guarantee proper measures will be observed it is indeed better not to hold them, probably this declaration just mean the organizers don't want to get involved in properly controlling them (which is fine, it would be much worse just to do it badly)

Large spectator events, indoors and out with no masks, are commonplace in the U.S. But herd immunity has been reached.

Even last year, though, socially distanced fans were allowed at football games. No issues with COVID.

For indoor events, proper ventilation would help. COVID from air travel was not an issue last year and some planes were packed like sardines. Or organizers could allow clapping only. Japanese will comply.