I haven't successfully deployed my app, but I did get around this error by downgrading rsconnect as per here Unable to deploy on shinyapp.io - #3 by OGORO. Specifically
remotes::install_version("rsconnect", "0.8.29")
and attempting to republish now gets me to this error:
Preparing to deploy application...DONE
Uploading bundle for application: 2...Warning:
DONE
Error in if (is.null(application$owner_username) || accountDetails$username == :
missing value where TRUE/FALSE needed
Calls: <Anonymous>