There was a query earlier regarding installing the binary RStudio debian package in debian buster.
https://community.rstudio.com/t/installing-rstudio-on-debian-buster/28126
After installation, Rstudio can't be started because of the missing libssl.so.1.0.2 in buster.
The following workaround worked for me:
Download the missing library from here
https://debian.pkgs.org/9/debian-main-amd64/libssl1.0.2_1.0.2r-1~deb9u1_amd64.deb.html
and install with the dpkg -i command.
Afterwards, restart Rstudio
Best Wishes
Frank