When tried to install through terminal command:
conda install -c r rstudio
The terminal got stuck in solving environmental step forever. I manually killed the process.
Then I tried to install Rstudio from anaconda-navigator by creating a new environment for R and python 3.7. The only available (listed) Rstudio version were from 1.0.44 and 1.1.456. I can install version 1.0.44 but not 1.1.456. Greater issue for me that the latest versions are not even listed.