The equivalent in R (RStudio is just an IDE for the R programming language) would be .Rmd (RMarkdown) or .qmd(Quarto) which is the next generation tool that supports not only R but Python, Julia and Observable
Rmarkdown is an R package, is mainly focused on R with some support for other languages but used from whitin the R ecosystem. Quarto on the other hand, is an independent software with different levels of integration with development tools like RStudio or VS Code and it is not focused specifically on R, it is meant to supersed RMarkdown in the future and most new developments are going to take place in Quarto but for the time being some specific applications are only possible in RMarkdown, for example, rendering websites with heavily customized themes is only possible with blogdown, which is an RMarkdown extension.
So, the right tool for the job is going to depend on what the job actually is.