There are manuals that you can find there.
R Studio (the IDE): https://www.rstudio.com/
R Studio cheat sheets: https://www.rstudio.com/resources/cheatsheets/
There is usually enough information on stack overflow / stack exchange to get through some questions. There is also a stats specific version that can sometimes be helpful. https://stats.stackexchange.com/
You are talking about documentation for user / community contributed packages. There is a minimum amount of standardization that needs to be followed, but yes, I do agree that the documentation could be better.
Hopefully this helps with installing packages: https://jtleek.com/modules/01_DataScientistToolbox/02_09_ins...
Regarding first timers, I think that once they’re aware of RStudio and the content they put out, learning becomes much more friendly and modern.
Still, I definitely agree and would appreciate a modern manual on base R.
Then I went looking for how to interact with JSON. There's no builtin library I guess but rjson seems to be what people use. There's no official documentation I can find on how to install a package but there are many blog posts. The rjson's only official documentation seems to be in PDF and again it's pretty minimal: https://cran.r-project.org/web/packages/rjson/rjson.pdf.
Again, to be fair, anyone looking into Common Lisp or Standard ML or OCaml would probably feel the exact same way about their ecosystems.
Does it cause a problem for existing users? Probably not. Is it the friendliest thing for first-timers to get into? Probably not. Is that a problem? Again probably not?