I'm saying it is more likely they knew he had COVID but thought cancelling / delaying would be a bad political move, and now are announcing it because it might achieve the opposite, concern and understanding.
This also might be a prelude to him stepping down in favor of another candidate or Harris.
So I think it's more likely it was known, and this is a calculated release of information.
Taiwanese citizens are in fact Chinese citizens because Taiwan is part of China, the political reality is more complex than I think people realize, but China considers Taiwan to be part of China.