I found it interesting that he tested possibly so many times including after when he “recovered”. If he is able to serve his entire term, and runs for reelection, i would not be surprised if Biden were to “get” Covid and he uses that as an excuse to not campaign and/or debate.
Despite reality, I wouldn't be surprised if you think the reason there is no presidential debate before 2022 is because Biden (or whoever is on the D ticket) is too scared/weak/corrupt/...
There is no reason why the two candidates' campaigns cannot directly set the terms of the debates. The commission unilaterally canceled the second debate in 2020 and unilaterally changed the terms of the debate to suit Biden's liking. The moderators they have chosen have not exactly been neutral, for example in 2016, one joined the Obama team days after moderating a debate, and opinion hosts have moderated debates.