On R studio home page, make sure to download the version 2021.09 Preview (as of writing of this blogpost, this is still in preview) and install this version on your client machine (supported windows machine, MacOS and Linux).
Once installation is completed, head to global options (Tools->Global options) and select Pane Layout. You will have a new set of buttons available (Add Column; Remove Column). With Add column an additional pane will be added to layout.
It’s not as convenient as the right-click –> “Split horizontally” or “Split vertically” that we get in tools like SSMS and VS Code, but I’m happy to see this change in R Studio.