As a side note, your release notes say
- No longer support Debian 9 (“stretch”) for Desktop, Server, and Workbench (#10981)
- No longer support SLES 12 for Desktop, Server, and Workbench (#10583)
But the download page you have linked says
Prerequisites RStudio Server requires Debian version 8 (or higher) or Ubuntu version 16.04 (or higher).