The 'latest' preview links still haven't been updated for the 1.4.x release.
wget https://rstudio.org/download/latest/preview/desktop/bionic/rstudio-latest-amd64.deb results in https://s3.amazonaws.com/rstudio-ide-build/desktop/bionic/amd64/rstudio-1.3.1093-amd64.deb being downloaded.
The previous issue regarding the updating of the urls is locked.